Automate Python triage membership.

[Mariatta]

It is possible to automate the process for adding people to the Python Triage Team.

1. A ticket is opened in core-workflow for adding a person to the triage team
2. Any core dev can approve the request by applying "approved" label
3. a bot (or script or GitHub App or GitHub Action) automatically invites the person to the team after seeing the "approved" label. It can expand upon the script in https://github.com/python/core-workflow/blob/master/utils/triage_team.py
   3.1 if "approved" label was not added by Python core team member, remove it.
4. bot automatically closes the issue after triager was invited.

Similar bot: https://github.com/python-trio/snekomatic

For this purpose the bot needs "admin" access to Python org.

For security reason, the access token or secret for the bot should be stored as environment variable, and visible only by select people.

Also for security reason, write access to the bot's code can be restricted to a small group of people only, instead of to all core developers.

[ezio-melotti]

I proposed something similar in python/devguide#848.