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

app/jobs/conversations/reopen_snoozed_conversations_job.rb

@@ -2,6 +2,6 @@ class Conversations::ReopenSnoozedConversationsJob < ApplicationJob
   queue_as :low
 
   def perform
-    Conversation.where(status: :snoozed).where(snoozed_until: 3.days.ago..Time.current).all.each(&:open!)
+    Conversation.where(status: :snoozed).where(snoozed_until: 3.days.ago..Time.current).all.find_each(batch_size: 100, &:open!)
   end
 end