Workflow rejection reasons are not properly encoded

[bruno-atmire]

Describe the bug
When an item is rejected in the workflow, the user has the option to provide a rejection "reason". That "reason" is not properly encoded when it is sent to the backend. In particular, the ampersand character causes the remainder of the message to be "ignored".
I was able to reproduce the bug on https://demo7.dspace.org/. The bug is located here.

To Reproduce
Steps to reproduce the behavior:

1. Set up a collection and assign yourself to the reviewers group (default DSpace workflow)
2. Add a new item to that collection
3. Reject the item and add special characters to the reason, e.g. &, @...
4. Submit the reason
5. Observe that the body of the POST request contains the specified reason, up until the first ampersand. Also observe that additional properties are sent that should not be present.
6. Submit the item again and this time accept it
7. Observe that in dc.description.provenance, the "rejection reason" is incomplete.

Expected behavior
The rejection reason should be encoded properly, such that it cannot be interpreted as a form parameter. Then the POST request will contain the complete message, and so will the provenance value. No changes are needed to the backend.

[benbosman]

@tdonohue this should be doable with 1 hour of work

[tdonohue]

Thanks @benbosman and @bruno-atmire for getting this added. I'll pull this into the 7.0 board with medium priority and assign to your team. That said, please do feel free to work on this once high priority tickets are all completed/in progress, as it seems like something that'd be good to fix in 7.0