[Iceberg] Session property for target split size

[ZacBlanco]

Description

Adds a session property for target split size.

Motivation and Context

Makes it easier to do performance debugging by setting the desired split size on a per-query basis.

Impact

New configuration property.

Test Plan

unit tests

Contributor checklist

• Please make sure your submission complies with our contributing guide, in particular code style and commit standards.
• PR description addresses the issue accurately and concisely. If the change is non-trivial, a GitHub Issue is referenced.
• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
• If release notes are required, they follow the release notes guidelines.
• Adequate tests were added if applicable.
• CI passed.

Release Notes

== RELEASE NOTES ==

Iceberg Connector Changes
* Add target_split_size session property :pr:`24417`

[steveburnett]

Thanks for the release note! Nit formatting suggestion.

== RELEASE NOTES ==

Iceberg Connector Changes
* Add ``target_split_size session`` property. :pr:`24417`

Consider documenting the new session property, perhaps in
https://github.com/prestodb/presto/blob/master/presto-docs/src/main/sphinx/connector/iceberg.rst#session-properties .