chore: Use find_each instead of .all.each (#6975)

- Enable the rubocop Rails/FindEach
- Replace the .all.each with .find_each

This should let us avoid potential memory usage.
Motivation from the speedshop newsletter by Nate Berkopec

ref: https://www.rubyinrails.com/2017/11/16/use-find-each-instead-of-all-each-in-rails/
ref: https://linear.app/chatwoot/issue/CW-1480/chore-run-all-sidekiq-jobs-async

.rubocop.yml

@@ -71,6 +71,10 @@ Rails/ApplicationController:
     - 'app/controllers/platform_controller.rb'
     - 'app/controllers/public_controller.rb'
     - 'app/controllers/survey/responses_controller.rb'
+Rails/FindEach:
+  Enabled: true
+  Include: 
+    - 'app/**/*.rb'
 Rails/CompactBlank:
   Enabled: false
 Rails/EnvironmentVariableAccess: