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/telegram/incoming_message_service.rb

@@ -45,7 +45,7 @@ class Telegram::IncomingMessageService
     return if @contact.avatar.attached?
 
     avatar_url = inbox.channel.get_telegram_profile_image(params[:message][:from][:id])
-    ::ContactAvatarJob.perform_later(@contact, avatar_url) if avatar_url
+    ::Avatar::AvatarFromUrlJob.perform_later(@contact, avatar_url) if avatar_url
   end
 
   def conversation_params