Filter incoming Create activities by relation to local activity (#10005)

Reject those from accounts with no local followers, from relays
that are not enabled, which do not address local accounts and are
not replies to accounts that do have local followers

app/services/activitypub/process_collection_service.rb

@@ -44,6 +44,7 @@ class ActivityPub::ProcessCollectionService < BaseService
   end
 
   def verify_account!
+    @options[:relayed_through_account] = @account
     @account = ActivityPub::LinkedDataSignature.new(@json).verify_account!
   rescue JSON::LD::JsonLdError => e
     Rails.logger.debug "Could not verify LD-Signature for #{value_or_id(@json['actor'])}: #{e.message}"