Refactor hard-coded messaging for approvals

Assigning myself for this one.

I worked on this today and pushed up my changes to the fork.

So far, this will programmatically create bundle fields on the message entity to store the request which generated the notification in question.

It also add configuration settings to the request type config entity to store a desired template.

Last, there's a small UX enhancement here. When transitioning a workspace and selecting reviewers, any previously created and pending requests will be checked and disabled to indicate that the request has already been made. And then those same unpublished requests will be republished here.

The next steps are to:

1. Work out why these tokens aren't being replaced in this message text:
   

   You have been requested to provide a [workspace_approval_request:bundle:entity:label] of the [site:name] <a href="label]">[workspace_approval_request:entity:subject:entity:label]</a> workspace.
   

2. Figure out why that text is only sent as the email subject and not the body

Posted some fixes to failing tests.

Great work. This module is really coming together.

heddn → closed merge request !3

Automatically closed - issue fixed for 2 weeks with no activity.