Improve the documentation for Notebook 7 (#6813)

* [pre-commit.ci] pre-commit autoupdate (#6814)

updates:
- [github.com/python-jsonschema/check-jsonschema: 0.21.0 → 0.22.0](python-jsonschema/check-jsonschema@0.21.0...0.22.0)
- [github.com/psf/black: 23.1.0 → 23.3.0](psf/black@23.1.0...23.3.0)
- [github.com/charliermarsh/ruff-pre-commit: v0.0.254 → v0.0.260](astral-sh/ruff-pre-commit@v0.0.254...v0.0.260)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

* Add note and warning on the extension landing page

* fix nbclassic url

* fix seealso blocks

* Fix note

* add changelog to the navbar

* update faq

* Update screencasts and screenshots

* Remove old screenshots and screencasts

* rename migrating file

* Split the migration guide

* dedicate a page to new features

* document themes

* Iterate on the new features

* expand docs on extensions

* add Binder link

* mention the interface dropdown

* iterate on features

* Mention nbgrader and RISE

* Lint

* Add server extension docs

* fixes

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: jtpio

docs/source/_static/images/blank-notebook-ui.png

@@ -4,6 +4,14 @@
 
 1. How do I install a prerelease version such as a beta or release candidate?
 
+You can install a prerelease version of the notebook using the `--pre` flag with `pip`:
+
 ```bash
 python -m pip install notebook --pre --upgrade
 ```
+
+If you are using `conda` or `mamba`, you can install a prerelease version of the notebook using the alpha or beta label. For example, to install the latest alpha release, you can run:
+
+```bash
+conda install -c conda-forge -c conda-forge/label/notebook_alpha notebook=7.0.0a18
+```

docs/source/_static/images/blank-notebook-ui.svg

@@ -6,12 +6,12 @@ This describes the basic steps to write a TypeScript extension for the Jupyter
 notebook front-end. This allows you to customize the behaviour of the various
 pages like the dashboard, the notebook, or the text editor.
 
-Starting with Notebook v7, front-end extensions for the notebook can be developed
+Starting with Notebook 7, front-end extensions for the notebook can be developed
 as prebuilt JupyterLab extensions.
 
-This means Notebook v7 is able to reuse many of the existing extensions from the JupyterLab ecosystem as is.
+This means Notebook 7 is able to reuse many of the existing extensions from the JupyterLab ecosystem as is.
 
-If you would like to develop a prebuilt extension for Notebook v7, check out:
+If you would like to develop a prebuilt extension for Notebook 7, check out:
 
 - [JupyterLab Extension Tutorial](https://jupyterlab.readthedocs.io/en/latest/extension/extension_tutorial.html): A tutorial to learn how to make a simple JupyterLab extension.
-- The [JupyterLab Extension Examples Repository](https://github.com/jupyterlab/extension-examples): A short tutorial series to learn how to develop extensions for JupyterLab by example.
+- The [JupyterLab Extension Examples Repository](https://github.com/jupyterlab/extension-examples): A repository containing many examples of JupyterLab extensions for performing various tasks: adding commands, adding a new widget, handling user settings, etc.

docs/source/_static/images/jupyter-file-editor.png

@@ -1,5 +1,20 @@
 # Extending the Notebook
 
+```{warning}
+Please note that the extension system for Notebook 7 is radically different
+from the one used in Notebook 6.5.x and earlier. If you are looking for
+information on how to extend the classic Notebook, please refer to the
+[documentation for NbClassic](https://nbclassic.readthedocs.io/en/latest/extending/index.html).
+```
+
+```{note}
+With Notebook 7 being developed on top of JupyterLab and Jupyter Server, the
+frontend extension system is now based on the same extension system used by JupyterLab.
+
+Server extensions are also now based on the same system used by Jupyter Server.
+You will find below a link to the relevant documentations.
+```
+
 Certain subsystems of the notebook server are designed to be extended or
 overridden by users. These documents explain these systems, and show how to
 override the notebook's defaults with your own custom behavior.