Add federation relay support (#7998)

* Add federation relay support

* Add admin UI for managing relays

* Include actor on relay-related activities

* Fix i18n

app/workers/activitypub/distribution_worker.rb

@@ -14,6 +14,8 @@ class ActivityPub::DistributionWorker
     ActivityPub::DeliveryWorker.push_bulk(inboxes) do |inbox_url|
       [signed_payload, @account.id, inbox_url]
     end
+
+    relay! if relayable?
   rescue ActiveRecord::RecordNotFound
     true
   end
@@ -24,6 +26,10 @@ class ActivityPub::DistributionWorker
     @status.direct_visibility?
   end
 
+  def relayable?
+    @status.public_visibility?
+  end
+
   def inboxes
     @inboxes ||= @account.followers.inboxes
   end
@@ -39,4 +45,10 @@ class ActivityPub::DistributionWorker
       adapter: ActivityPub::Adapter
     ).as_json
   end
+
+  def relay!
+    ActivityPub::DeliveryWorker.push_bulk(Relay.enabled.pluck(:inbox_url)) do |inbox_url|
+      [signed_payload, @account.id, inbox_url]
+    end
+  end
 end

app/workers/activitypub/update_distribution_worker.rb

@@ -9,7 +9,11 @@ class ActivityPub::UpdateDistributionWorker
     @account = Account.find(account_id)
 
     ActivityPub::DeliveryWorker.push_bulk(inboxes) do |inbox_url|
-      [payload, @account.id, inbox_url]
+      [signed_payload, @account.id, inbox_url]
+    end
+
+    ActivityPub::DeliveryWorker.push_bulk(Relay.enabled.pluck(:inbox_url)) do |inbox_url|
+      [signed_payload, @account.id, inbox_url]
     end
   rescue ActiveRecord::RecordNotFound
     true
@@ -21,6 +25,10 @@ class ActivityPub::UpdateDistributionWorker
     @inboxes ||= @account.followers.inboxes
   end
 
+  def signed_payload
+    @signed_payload ||= Oj.dump(ActivityPub::LinkedDataSignature.new(payload).sign!(@account))
+  end
+
   def payload
     @payload ||= ActiveModelSerializers::SerializableResource.new(
       @account,