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.

spec/controllers/api/v1/accounts/contacts_controller_spec.rb

@@ -487,6 +487,14 @@ RSpec.describe 'Contacts API', type: :request do
         contact.reload
         expect(contact.avatar.attached?).to be(true)
       end
+
+      it 'updated avatar with avatar_url' do
+        patch "/api/v1/accounts/#{account.id}/contacts/#{contact.id}",
+              params: valid_params.merge(avatar_url: 'http://example.com/avatar.png'),
+              headers: admin.create_new_auth_token
+        expect(response).to have_http_status(:success)
+        expect(Avatar::AvatarFromUrlJob).to have_been_enqueued.with(contact, 'http://example.com/avatar.png')
+      end
     end
   end