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

Gemfile.lock

@@ -16,8 +16,6 @@ GIT
 GEM
   remote: https://rubygems.org/
   specs:
-    action-cable-testing (0.6.1)
-      actioncable (>= 5.0)
     actioncable (6.0.3.7)
       actionpack (= 6.0.3.7)
       nio4r (~> 2.0)
@@ -613,7 +611,6 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  action-cable-testing
   activerecord-import
   acts-as-taggable-on
   administrate