[WIP] Configure Firefox :: Messaging System bugs for automatic triage

[dmose]

Configures Firefox :: Messaging System bugs for automatic triage.

This patch is still Work In Progress. From my notes, what needs to happen is this:

• In bugbot, change the component list from "component": "New Tab Page" to "component": ["New Tab Page", "Messaging System"].
• Related to above, some doc changes in frontend_triage.py, and check_rules_on_wiki.py.

Checklist

• Type annotations added to new functions
• Docs added to functions touched in main classes
• Dry-run produced the expected results
• The to-be-announced tag added if this is worth announcing