After 7 days of repeated delivery failures, give up on inbox (#5131)

- A successful delivery cancels it out
- An incoming delivery from account of the inbox cancels it out

app/workers/activitypub/delivery_worker.rb

@@ -15,7 +15,10 @@ class ActivityPub::DeliveryWorker
     perform_request
 
     raise Mastodon::UnexpectedResponseError, @response unless response_successful?
+
+    failure_tracker.track_success!
   rescue => e
+    failure_tracker.track_failure!
     raise e.class, "Delivery failed for #{inbox_url}: #{e.message}", e.backtrace[0]
   end
 
@@ -34,4 +37,8 @@ class ActivityPub::DeliveryWorker
   def response_successful?
     @response.code > 199 && @response.code < 300
   end
+
+  def failure_tracker
+    @failure_tracker ||= DeliveryFailureTracker.new(@inbox_url)
+  end
 end