Issue with request of embed objects, where object cache entry is missing

[atarix83]

During implementation of https://github.com/DSpace/dspace-angular/issues/601 I encountered several issues with request of embed objects. In many case when the request is already fetched by rest, the payload returned is undefined due to a missing object cache entry in the cache. Objects cache should exist for this requests because are not expired, as a result the request is not dispatched again. Probably this issue is related to https://github.com/DSpace/dspace-angular/issues/626

[tdonohue]

Encountered again in testing of #1641. Here's how to reproduce problem easily:

• Login as an Admin
• Edit an Item
• Edit Item Policies
• Change default "Anonymous" READ policy to be "Administrator" READ (i.e. change the group assigned to the policy)
• Change will be successful, but on the Policies page the group with disappear. See screenshot at https://github.com/DSpace/dspace-angular/pull/1641#pullrequestreview-977195916)
• If you reload the page in the browser, you'll see the group is now "Administrator".

This results in a usability issue (described in more detail in #1753). The current code in this scenario works, but this bug makes it appear to have failed.

Flagging this as high priority and pulling over to the 7.4 board.

[tdonohue]

Adding a zero hour estimate to this ticket as this will be completed alongside #1753 (and the estimate in that ticket includes this one)