Automatic merge from submit-queue

Expose Changesets (transactions) in dns provider

This makes the dnsprovider usable in more scenarios, and it also solves
some TODOs in the federation code.

WIP  - I'm going to test this to make sure this both works and is sufficient for use in my dns controller, but I wanted to put some code behind the talk in #28477.  cc @quinton-hoole 

Issue #28477