Support relative paths in pyproject.toml's [tool.esbonio.sphinx.pythonCommand]

[neongreen-sc]

What would you like to see

Right now it seems like paths have to be absolute; would be great if I could specify a path relative to the pyproject.toml file (to make life easier now that VSCode python env is no longer inherited)

[neongreen-sc]

(although given that the paths are different between Windows and Linux anyway.. I suppose it doesn't help that much, compared to smth like "let me just give a path to .venv"? which is harder to implement)

[alcarney]

I agree that the experience with esbonio.sphinx.pythonCommand and venvs is not ideal at the moment. I have been thinking about adding a config syntax like ${venv:/path/to/env} which would expand to /path/to/env/bin/python or path/to/env/Scripts/python.exe depending on the current OS.

As for the relative path, perhaps it's a simple as extending #847 to also cover esbonio.sphinx.pythonCommand? 🤔