Copy the keys to secrets manager when switching

[brichet]

This PR fixes an issue raised in #200 (comment).

When switching the setting to use the secrets manager, the API keys stored in the settings are replaced with '***', and we expect the secrets manager to have the keys. If not, we'll have to type them again.

With this PR, switching to use the secrets manager check if their is already an associate key in the secrets manager, and if not set the current one their. That way, the secrets is not lost.

It also fixes:

• display the alert when the secrets manager is on (instead of off) to advertise of not using it
• never populate the API key field with the value from setting when using the secrets manager. This avoid having '***' in this field if the API key is not in the manager.

[nakul-py]

When switching the setting to use the secrets manager, the API keys stored in the settings are replaced with '***', and we expect the secrets manager to have the keys. If not, we'll have to type them again.

But also when we reloads our localhost I think it does not saves API key so we have to also write API key again and another thing is currently chat history is not saved so when reloads it also erase all data.

[brichet]

But also when we reloads our localhost I think it does not saves API key so we have to also write API key again and another thing is currently chat history is not saved so when reloads it also erase all data.

Indeed, it's all in memory by default. There is currently no solution for the persistence of the chat messages, not sure that we want to save all this information in the browser, though.

For API keys persistence, one can:

• disable the secrets manager, but the keys will be saved in plain text using the settings system of jupyterlab (file on server if using jupyterlab, local storage of the browser if using jupyterlite)
• provide a secrets connector from an plugin. There is some description here but we definitely need to improve it