UI3 - Try making puma metrics work by probing in puma workers (#12248)

Testing #12238 in a non prod
environment (i.e. UI3)

Follow instructions in
https://docs.appsignal.com/ruby/integrations/puma.html#usage-with-preload_app

Author: albertchae

config/puma.rb

@@ -51,3 +51,14 @@
 require_relative "../app/lib/credentials"
 
 Credentials.load if ENV["DOPPLER_TOKEN"]
+
+# https://docs.appsignal.com/ruby/integrations/puma.html#usage-with-preload_app
+# Add this before_fork callback to stop the minutely probes in the Puma main process
+before_fork do
+  Appsignal::Probes.stop
+end
+
+# Add this on_worker_boot callback to start the minutely probes in the Puma worker processes
+on_worker_boot do
+  Appsignal::Probes.start
+end