Fixes #6182 - Dynflowized repository update

- [x] Dynflowize repository update
- [x] Fix old tests
- [x] Make new tests
I'm ok with this implementation + https://github.com/Katello/katello/pull/4488 will address having this as part of the product orchestration. We could probably use `async_task` here, as it doesn't seem to require the sync for here