FEATURE: allow post process mutex to be held longer

Previously we would only hold the post process mutex for 1 minute, that is
not enough when processing a post with lots of images. This raises the bar
to 10 minutes.

It also cleans up error reporting around distributed mutexes expiring. We
used to double report.

lib/cooked_post_processor.rb

@@ -35,7 +35,7 @@ class CookedPostProcessor
   end
 
   def post_process(bypass_bump: false, new_post: false)
-    DistributedMutex.synchronize("post_process_#{@post.id}") do
+    DistributedMutex.synchronize("post_process_#{@post.id}", validity: 10.minutes) do
       DiscourseEvent.trigger(:before_post_process_cooked, @doc, @post)
       remove_full_quote_on_direct_reply if new_post
       post_process_oneboxes