feat: add index to conversation id and account_id (#6757)

- This PR adds an index to conversations id and account_id. This improves the performance of some reports query

db/migrate/20230327081350_add_index_to_conversations_account_id_and_id.rb

@@ -0,0 +1,7 @@
+class AddIndexToConversationsAccountIdAndId < ActiveRecord::Migration[6.1]
+  disable_ddl_transaction!
+
+  def change
+    add_index :conversations, [:account_id, :id], name: 'index_conversations_on_id_and_account_id', algorithm: :concurrently
+  end
+end