Change pythonPath to pythonCommand in the pygls-playground extension

[alcarney]

Description

This allows the user to specify an arbitrary command to use when launching the python interpreter. When combined with tools like uv, this makes it trivial to switch between different versions of pygls!

For example

{
  "pygls.server.pythonCommand": ["uv", "run", "--no-project", "--prerelease=allow", "--with", "pygls==2.0a2", "python"]
}

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

Automated linters

You can run the lints that are run on CI locally with:

uv run --all-extras poe lint

[alcarney]

Thanks!