fix: ensure server commands can be executed

[alcarney]

This brings back the ability to execute commands provided by the language server in the vscode-playground extension.

Instead of encoding all the commands in the package.json file, the extension inspects the ServerCapabilities of the initialize response to determine which commands a server provides. It then presents a quick pick list of commands the user can choose to run.

This should mean commands (that don't take any arguments at least) now "just work" with the playground extension

This PR also re-defines the example configuration keys in the packae.json for json_server.py otherwise VSCode simply responds with null when the configuration values are requested

Closes #365

Code review checklist (for code reviewer to complete)

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Commit messages are meaningful (see this for details)
• Tests have been included and/or updated, as appropriate
• Docstrings have been included and/or updated, as appropriate
• Standalone docs have been updated accordingly

[alcarney]

The poetry install for windows+python 3.12 seems a little flakey too
https://github.com/openlawlibrary/pygls/actions/runs/6052781183/job/16426922189?pr=368#step:4:67

Though since 3.12 is still a pre-release perhaps that's to be expected! :)

[tombh]

Ah yes, I've added that to the #367 falkey tracking issue 😅