Add a spam check (#11217)

* Add a spam check

* Use Nilsimsa to generate locality-sensitive hashes and compare using Levenshtein distance

* Add more tests

* Add exemption when the message is a reply to something that mentions the sender

* Use Nilsimsa Compare Value instead of Levenshtein distance

* Use MD5 for messages shorter than 10 characters

* Add message to automated report, do not add non-public statuses to
automated report, add trust level to accounts and make unsilencing
raise the trust level to prevent repeated spam checks on that account

* Expire spam check data after 3 months

* Add support for local statuses, reduce expiration to 1 week, always create a report

* Add content warnings to the spam check and exempt empty statuses

* Change Nilsimsa threshold to 95 and make sure removed statuses are removed from the spam check

* Add all matched statuses into automatic report

config/locales/en.yml

@@ -875,6 +875,8 @@ en:
     profile: Profile
     relationships: Follows and followers
     two_factor_authentication: Two-factor Auth
+  spam_check:
+    spam_detected_and_silenced: This is an automated report. Spam has been detected and the sender has been silenced automatically. If this is a mistake, please unsilence the account.
   statuses:
     attached:
       description: 'Attached: %{attached}'