Update codebase for modern Python and Wikimedia needs
- Codebase converted from Python2 (sunset upstream since January 1, 2020) to Python3 (3.9 specifically)
- 3rd-party libraries upgraded
- Wiki replica queries updated for T167246: Refactor "user" & "user_text" fields into "actor" reference table
- Wiki replica queries updated for T166732: Refactor comment storage in the database and abstract access in MediaWiki
- Removed "New edit with hashtag" trigger. See T250363#8608260
- Removed "Most edited articles" trigger. See https://www.mediawiki.org/wiki/Reading/Web/Projects/Edit_based_trending_service
Bug: T294448