Allow commands to have optional descriptions to be used for similar commands feature

[luabud]

It'd be nice if extensions could contribute with optional descriptions for commands so it can be used when computing similar commands.

For example, for the Python extension we have the "Python: Create Environment" command, and it'd be super convenient if it showed up when typing "venv" or "conda" in the command palette. With the ability of including optional descriptions, we might be able to add terms we know are relevant to specific commands.

[joyceerhl]

This would also be nice to have for Remote Repositories