Add CLI task for rotating keys (#8466)

* If an Update is signed with known key, skip re-following procedure

Because it means the remote actor did *not* lose their database

* Add CLI method for rotating keys

    bin/tootctl accounts rotate [USERNAME]

Generates a new RSA key per account and sends out an Update activity
signed with the old key.

* Key rotation: Space out Update fan-outs every 5 minutes per 1000 accounts

* Skip suspended accounts in key rotation

app/lib/activitypub/activity/update.rb

@@ -11,6 +11,6 @@ class ActivityPub::Activity::Update < ActivityPub::Activity
 
   def update_account
     return if @account.uri != object_uri
-    ActivityPub::ProcessAccountService.new.call(@account.username, @account.domain, @object)
+    ActivityPub::ProcessAccountService.new.call(@account.username, @account.domain, @object, signed_with_known_key: true)
   end
 end