Refactors `TrustLevel` and moves translations from server to client
Additional changes:
* "staff" and "admin" wasn't translatable in site settings
* it replaces a concatenated string with a translation
* uses translation for trust levels in users_by_trust_level report
* adds a DB migration to rename keys of translation overrides affected by this commit
Zeitwerk simplifies working with dependencies in dev and makes it easier reloading class chains.
We no longer need to use Rails "require_dependency" anywhere and instead can just use standard
Ruby patterns to require files.
This is a far reaching change and we expect some followups here.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
