Fix #6250 - improve JobQueueFactory performance

[glennmatthews]

Closes #6250

What's Changed

Improve efficiency of JobQueueFactory.jobs method by:

• using many-to-many .set() instead of iterating over the queryset and repeatedly calling .add()
• only updating affected Jobs if they haven't already been flagged.

TODO

• [x] Explanation of Change(s)
• [x] Added change log fragment(s) (for more information see the documentation)
• n/a Attached Screenshots, Payload Example
• [x] Unit, Integration Tests
• n/a Documentation Updates (when adding/changing features)
• n/a Example App Updates (when adding/changing features)
• [x] Outline Remaining Work, Constraints from Design