ActivityPub migration procedure (#4617)

* ActivityPub migration procedure

Once one account is detected as going from OStatus to ActivityPub,
invalidate WebFinger cache for other accounts from the same domain

* Unsubscribe from PuSH updates once we receive an ActivityPub payload

* Re-subscribe to PuSH unless already unsubscribed, regardless of protocol

app/controllers/activitypub/inboxes_controller.rb

@@ -7,6 +7,7 @@ class ActivityPub::InboxesController < Api::BaseController
 
   def create
     if signed_request_account
+      upgrade_account
       process_payload
       head 201
     else
@@ -24,6 +25,11 @@ class ActivityPub::InboxesController < Api::BaseController
     @body ||= request.body.read
   end
 
+  def upgrade_account
+    return unless signed_request_account.subscribed?
+    Pubsubhubbub::UnsubscribeWorker.perform_async(signed_request_account.id)
+  end
+
   def process_payload
     ActivityPub::ProcessingWorker.perform_async(signed_request_account.id, body.force_encoding('UTF-8'))
   end