Move how Python environments activate docs to website

[Tyriar]

Context: microsoft/vscode-python#21793 (comment)

• Currently https://aka.ms/vscodePythonTerminalActivation points at https://github.com/microsoft/vscode-python/wiki/Activate-Environments-in-Terminal-Using-Environment-Variables
  We should move this to the actual docs website since it's official documentation intended for the user.
• Document the limitation of deactivate command not working.
• We should also update any docs related to Python: Use environment variables defined in .env file when running code in a terminal vscode-python#944 (comment)

[karrtikr]

@gregvanl Curious, how often are "vscode-docs" deployed from main branch?

[gregvanl]

@karrtikr We publish manually as needed and usually the same day as a PR is merged to vscode-docs main.