Add voters count support (#11917)

* Add voters count to polls

* Add ActivityPub serialization and parsing of voters count

* Add support for voters count in WebUI

* Move incrementation of voters count out of redis lock

* Reword “voters” to “people”

config/locales/en.yml

@@ -1030,6 +1030,9 @@ en:
       private: Non-public toot cannot be pinned
       reblog: A boost cannot be pinned
     poll:
+      total_people:
+        one: "%{count} person"
+        other: "%{count} people"
       total_votes:
         one: "%{count} vote"
         other: "%{count} votes"