Add a dedicated settings panel

[brichet]

Problem

Each provider has its own settings in @langchainjs.
Therefore, we need to update manually the settings when changing the provider.

Proposed Solution

Have a dedicated AI settings panel that does not use the Jupyterlab settings system, to give more flexibility.

Additional context

Discussion started at #27 (comment)

[jtpio]

Maybe it could be worth having a UI similar to what jupyter-ai provides. So the settings can be discovered via the chat panel.

Not sure how reusable the jupyter-ai components are though at the moment.

[jtpio]

Also a dedicated panel would help have better control on the persistence of secrets such as API keys and allow for temporary secrets valid until the next page refresh. Instead of relying on the settings which get stored in the browser in the case of JupyterLite, on the server for JupyterLab.

[jtpio]

Also opened #37, which could be done after the move to a proper panel.

The plugin providing the settings panel could then depend on the plugin providing the secrets manager.

[jtpio]

Maybe a good starting point could be to have something similar to what Jupyter AI does in the upcoming v3 version (or even reuse some parts of it if possible):

[jtpio]

Also maybe it could be useful to provide instructions for using the model in the settings panel directly.

For now the README has some information about some of the models, but it could be more practical to put that information somewhere in the settings panel directly (or hidden by default, but can be displayed easily).

For example in the case of ChromeAI that would allow putting links to access and enable the required flags.

[brichet]

Also maybe it could be useful to provide instructions for using the model in the settings panel directly.

For now the README has some information about some of the models, but it could be more practical to put that information somewhere in the settings panel directly (or hidden by default, but can be displayed easily).

For example in the case of ChromeAI that would allow putting links to access and enable the required flags.

Right, this helper could be updated when changing the provider.

I'll try to start that settings panel soon.