Move apache.iceberg provider to new providers structure

[potiuk]

This also add the feature of managing devel-dependencies via dependency groups in pyproject.toml and adjust tests to cover case where providers can be two levels deeper.

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[potiuk]

Did I say I love 💔 sphinx .... ?

[potiuk]

OK. I think I got to an agreement with Sphinx finally 🤞 ...

I also moved "example_dags" (i.e. system tests) from tests.system.providers.<provider_id> to tests.system.<provider_id>. I realized that tests.system. packages were previously exposed via inventory - and if there are any cross-providers references in the documentation, that would break the documentation links cross-providers. And we do not really need that extra "providers" package in the middle.

I moved the airbyte system tests back as well in this change.

This is the current apache.iceberg provider's inventory:

root@986a47c0f1f9:/opt/airflow/docs/_inventory_cache# python3 -m sphinx.ext.intersphinx apache-airflow-providers-apache-iceberg/objects.inv
py:attribute
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.conn_id                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.conn_id
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.conn_name_attr                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.conn_name_attr
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.conn_type                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.conn_type
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.default_conn_name                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.default_conn_name
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.hook_name                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.hook_name
py:class
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook
py:data
    airflow.providers.apache.iceberg.__version__                                         : _api/airflow/providers/apache/iceberg/index.html#airflow.providers.apache.iceberg.__version__
    airflow.providers.apache.iceberg.hooks.iceberg.TOKENS_ENDPOINT                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.TOKENS_ENDPOINT
    tests.system.apache.iceberg.example_iceberg.bash_command                                         : _api/tests/system/apache/iceberg/example_iceberg/index.html#tests.system.apache.iceberg.example_iceberg.bash_command
    tests.system.apache.iceberg.example_iceberg.test_run                                         : _api/tests/system/apache/iceberg/example_iceberg/index.html#tests.system.apache.iceberg.example_iceberg.test_run
py:method
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.get_conn                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.get_conn
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.get_token_macro                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.get_token_macro
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.get_ui_field_behaviour                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.get_ui_field_behaviour
    airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.test_connection                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#airflow.providers.apache.iceberg.hooks.iceberg.IcebergHook.test_connection
py:module
    airflow.providers.apache.iceberg                                                 : _api/airflow/providers/apache/iceberg/index.html#module-airflow.providers.apache.iceberg
    airflow.providers.apache.iceberg.hooks                                           : _api/airflow/providers/apache/iceberg/hooks/index.html#module-airflow.providers.apache.iceberg.hooks
    airflow.providers.apache.iceberg.hooks.iceberg                                         : _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html#module-airflow.providers.apache.iceberg.hooks.iceberg
    tests.system.apache.iceberg                                                      : _api/tests/system/apache/iceberg/index.html#module-tests.system.apache.iceberg
    tests.system.apache.iceberg.example_iceberg                                         : _api/tests/system/apache/iceberg/example_iceberg/index.html#module-tests.system.apache.iceberg.example_iceberg
std:doc
    _api/airflow/providers/apache/iceberg/hooks/iceberg/index airflow.providers.apache.iceberg.hooks.iceberg: _api/airflow/providers/apache/iceberg/hooks/iceberg/index.html
    _api/airflow/providers/apache/iceberg/hooks/index airflow.providers.apache.iceberg.hooks  : _api/airflow/providers/apache/iceberg/hooks/index.html
    _api/airflow/providers/apache/iceberg/index airflow.providers.apache.iceberg        : _api/airflow/providers/apache/iceberg/index.html
    _api/tests/system/apache/iceberg/example_iceberg/index tests.system.apache.iceberg.example_iceberg: _api/tests/system/apache/iceberg/example_iceberg/index.html
    _api/tests/system/apache/iceberg/index   tests.system.apache.iceberg             : _api/tests/system/apache/iceberg/index.html
    changelog                                Changelog                               : changelog.html
    commits                                  Package apache-airflow-providers-apache-iceberg: commits.html
    connections                              Connecting to Iceberg                   : connections.html
    index                                    apache-airflow-providers-apache-iceberg : index.html
    installing-providers-from-sources        Installing from sources                 : installing-providers-from-sources.html
    security                                 Releasing security patches              : security.html
std:label
    genindex                                 Index                                   : genindex.html
    howto/connection:iceberg                 Connecting to Iceberg                   : connections.html#howto-connection-iceberg
    modindex                                 Module Index                            : py-modindex.html
    py-modindex                              Python Module Index                     : py-modindex.html
    search                                   Search Page                             : search.html