Add ability to limit the number of documents allowed in Attachment fields in CLM Document Generation

Although this can be handled in workflow post submission, there are times when we need to ensure that only one document is added at the outset.

One common example of this would be those cases where users are asked to pick a document in CLM that is the parent document of the one being generated (e.g. an Amendment form). In this case it makes more sense if the user could only pick one document.

This requirement come up time and time again.