Investigate where we should implicitly trigger the `Python: Create Environment` command

[brettcannon]

Two options:

1. Prompt the user if they want to create an environment
2. If there is a pyproject.toml or requirements.txt file in the workspace, run the Create Environment command (or ask the user to select a virtual environment or create environment)

[luabud]

We can start with option 2 as it shouldn't be hard to expand it to 1 if we want to?

[karrtikr]

Related: #4606. If we were to add such a prompt it could be used here.