housekeep: TU rename

Renaming of Trusted User to Package Maintainer.

ToDo (code):

• Variables, values and strings in DB - Trusted User(s)
• UI elements and translations - Trusted User(s)
• Test cases (test_tu_...)
• Comments
• Anything referencing TU, TUs
• Table / Column names
• Routes (rename)

ToDo (other projects / dependent changes):

• Bylaws rename (tu-bylaws!6)
• MR to be created at infra for nginx config changes (bylaws url, /tu redirect) / combine with new release

Related issues/MRs: #446 (closed), tu-bylaws!6