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/models/concerns/avatarable.rb

@@ -7,19 +7,24 @@ module Avatarable
   included do
     has_one_attached :avatar
     validate :acceptable_avatar, if: -> { avatar.changed? }
+    after_save :fetch_avatar_from_gravatar
   end
 
   def avatar_url
     return url_for(avatar.representation(resize: '250x250')) if avatar.attached? && avatar.representable?
 
-    if [SuperAdmin, User, Contact].include?(self.class) && email.present?
-      hash = Digest::MD5.hexdigest(email)
-      return "https://www.gravatar.com/avatar/#{hash}?d=404"
-    end
-
     ''
   end
 
+  def fetch_avatar_from_gravatar
+    return unless saved_changes.key?(:email)
+    return if email.blank?
+
+    # Incase avatar_url is supplied, we don't want to fetch avatar from gravatar
+    # So we will wait for it to be processed
+    Avatar::AvatarFromGravatarJob.set(wait: 30.seconds).perform_later(self, email)
+  end
+
   def acceptable_avatar
     return unless avatar.attached?