Add the Plugin Manager

[jtpio]

Problem

In JupyterLab 4.1 there is a new plugin manager to make it easier to inspect the list of available plugins, and disable them:

• https://jupyterlab.readthedocs.io/en/latest/getting_started/changelog.html#plugin-manager
• https://jupyterlab.readthedocs.io/en/latest/user/extensions.html#managing-plugins-with-plugin-manager

Proposed Solution

Add the plugin manager, or at least some parts of it. At least enabling the widget to show the list of available plugins would already be useful.

The feature in JupyterLab also includes server side logic to manage the plugins (enable or disable). We may want to implement something similar in lite. Although that would likely involve storing the state of plugins in the user browser, and make that available in the application entrypoint (index.js).

Additional context

This was added to JupyterLab in jupyterlab/jupyterlab#14536