Make the Jupyter supervisor the default in non-desktop Positron configurations

[jmcphers]

This change makes Kallichore the default in non-desktop configurations of Positron, such as on Posit Workbench. In addition to the configuration change, it includes a number of other changes that improve the stability of the supervisor integration in order to bring it up to the quality needed.

In particular:

• The supervisor's behavior around session starting has changed; the RPC that starts sessions now doesn't return until the session has fully started and returned kernel information. We pick up this kernel info in Positron rather than making our own RPC for kernel info (when starting for the first time).
• We now hold any attempts to make UI Comm requests until the UI Comm has opened. This eliminates a lot of setConsoleWidth errors in the logs.
• The Kallichore terminal is now hidden by default.
• The R and Python extensions no longer have a hard dependency on the Jupyter Adapter extension. This allows them to work even when the Jupyter Adapter is unbootable (such as on REHL 9 or other systems where there are glibc issues with ZeroMQ)

Addresses #4941.

QA Notes

If logging issues, it's helpful to include the Kallichore logs, so run with the "Show Terminal" setting (added in this PR) turned on.

[sharon-wang]

LGTM!

I can confirm that Kallichore was enabled by default, with its Terminal hidden in Positron Server Web. After enabling the option to show the Kallichore Terminal and restarting Server Web, the Terminal became visible. I played around with starting, stopping and restarting Python and R Consoles and all was well 👍

On Desktop, Kallichore was not enabled by default as expected. Toggling the settings to enable Kallichore and show its Terminal also worked as expected.

I haven't had a chance to test this on Workbench yet though.