chore: Ability to Disable Gravatars (#5027)

fixes: #3853

- Introduced DISABLE_GRAVATAR Global Config, which will stop chatwoot from making API requests to gravatar
- Cleaned up avatar-related logic and centralized it into the avatarable concern
- Added specs for the missing cases
- Added migration for existing installations to move the avatar to attachment, rather than making the API that results in 404.

app/services/twitter/webhooks_base_service.rb

@@ -30,6 +30,6 @@ class Twitter::WebhooksBaseService
       user['id'], user['name'], additional_contact_attributes(user)
     )
     @contact = @contact_inbox.contact
-    ContactAvatarJob.perform_later(@contact, user['profile_image_url']) if user['profile_image_url']
+    Avatar::AvatarFromUrlJob.perform_later(@contact, user['profile_image_url']) if user['profile_image_url']
   end
 end