Support "Developer: Open Process Explorer"

## What is your suggestion?

Add something that can be used directly from the code-server UI to inspect the process tree under the remote `code-server` process. Ideally literally "Developer: Open Process Explorer" from VS code.

## Why do you want this feature?

Helpful to understand where memory is going - both from the angle of diagnosing processes spawned in extensions and taking stock of various user-spawned processes.

## Are there any workarounds to get this functionality today?

Sort of - you can manually figure out the same type of information from the OS.

## Are you interested in submitting a PR for this?

Yes, but would need some pointers. If this just isn't possible, that's OK and fine to close this issue 😄

Start by comparing the existing code-server UI with VS Code's "Developer: Open Process Explorer" command and determine whether the command can inspect the remote code-server process tree. Define the remote process data and UI integration needed; done means the command is available from code-server and displays the relevant process hierarchy.

Written by the indexing model from the issue text.