chore: Automate conversation display_id generation with db triggers (#1412)

Automate conversation display_id generation with db triggers

Co-authored-by: Saurabh Mehta <saurabh1.mehta@airtel.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>

spec/models/message_spec.rb

@@ -13,6 +13,7 @@ RSpec.describe Message, type: :model do
     let(:message) { build(:message, account: create(:account)) }
 
     it 'updates conversation last_activity_at when created' do
+      message.save!
       expect(message.created_at).to eq message.conversation.last_activity_at
     end