Send email when user group expiry date is updated

Send email notification on member expiry date update.

The following discussion from !50217 (merged) should be addressed:

• @manojmj started a discussion: (+1 comment)

  Hmm, I think this is going to be problematic.

  If we look at the email content being sent out in notification_service.update_group_member, it talks about changes to access level of the member only and nothing about expiry date. If we trigger the same email for expiry date changes too, it would confuse the email recipients and that would be wrong.

  Best would be to not make the changes in group_member.rb for post_update_hook and only make further changes in ee/group_member.rb, so like

      override :post_update_hook
      def post_update_hook
        super # takes care of email delivery for access changes alone
  
        if saved_change_to_access_level? || saved_change_to_expires_at?
          execute_hook_for(:update)
        end
      end

  WDYT? 🙂

  Also, given that we are now discussing this, it would be a good idea to create a follow-up for email notifications on member expiry date updates too 🙂