chore: Additional indexes and fixes (#6675)

- Fix breakage related to the look-up job in Heroku deploys 
- Add additional db indexes for performance optimisations

db/migrate/20230315105847_add_indexes_for_common_queries.rb

@@ -0,0 +1,11 @@
+class AddIndexesForCommonQueries < ActiveRecord::Migration[6.1]
+  # disabling ddl transaction is required for concurrent index creation
+  # https://thoughtbot.com/blog/how-to-create-postgres-indexes-concurrently-in
+  disable_ddl_transaction!
+
+  def change
+    ActiveRecord::Migration[6.1].add_index(:inboxes, [:channel_id, :channel_type], algorithm: :concurrently)
+    ActiveRecord::Migration[6.1].add_index(:conversations, [:account_id, :inbox_id, :status, :assignee_id], name: 'conv_acid_inbid_stat_asgnid_idx',
+                                                                                                            algorithm: :concurrently)
+  end
+end