chore: Migrate mailers from the worker to jobs (#12331)

Previously, email replies were handled inside workers. There was no
execution logs. This meant if emails silently failed (as reported by a
customer), we had no way to trace where the issue happened, the only
assumption was “no error = mail sent.”

By moving email handling into jobs, we now have proper execution logs
for each attempt. This makes it easier to debug delivery issues and
would have better visibility when investigating customer reports.

Fixes
https://linear.app/chatwoot/issue/CW-5538/emails-are-not-sentdelivered-to-the-contact

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

config/initializers/sidekiq.rb

@@ -6,9 +6,21 @@ Sidekiq.configure_client do |config|
   config.redis = Redis::Config.app
 end
 
+# Logs whenever a job is pulled off Redis for execution.
+class ChatwootDequeuedLogger
+  def call(_worker, job, queue)
+    Sidekiq.logger.info("Dequeued #{job['class']} #{job['jid']} from #{queue}")
+    yield
+  end
+end
+
 Sidekiq.configure_server do |config|
   config.redis = Redis::Config.app
 
+  config.server_middleware do |chain|
+    chain.add ChatwootDequeuedLogger
+  end
+
   # skip the default start stop logging
   if Rails.env.production?
     config.logger.formatter = Sidekiq::Logger::Formatters::JSON.new