chore: ability to run Chatwoot as API only server (#2344)

- Ability to run chatwoot as an API only server
- Removes action cable testing gem since it is merged to rails 6

spec/rails_helper.rb

@@ -66,6 +66,7 @@ RSpec.configure do |config|
   config.include SlackStubs
   config.include Devise::Test::IntegrationHelpers, type: :request
   config.include ActiveSupport::Testing::TimeHelpers
+  config.include ActionCable::TestHelper
 end
 
 Shoulda::Matchers.configure do |config|