Fix resolving accounts sometimes creating duplicate records for a given AP id (#15364)

* Fix ResolveAccountService accepting mismatching acct: URI

* Set attributes that should be updated regardless of suspension

* Fix key fetching

* Automatically merge remote accounts with duplicate `uri`

* Add tests

* Add "tootctl accounts fix-duplicates"

Finds duplicate accounts sharing a same ActivityPub `id`, re-fetch them and
merge them under the canonical `acct:` URI.

Co-authored-by: Claire <claire.github-309c@sitedethib.com>