[api] call the event jobs delayed

As we keep a transaction open for 1000 events, we lock quite some tables
to parse issues, clear cache lines, ...

src/api/app/models/event/base.rb

@@ -126,7 +126,7 @@ def notify_backend
     def perform_create_jobs
       self.create_jobs.each do |job|
         obj = job.to_s.camelize.safe_constantize.new(self)
-        obj.perform
+        obj.delay.perform
       end
     end