a8n: Make fast path in UpdateCampaign faster by only talking to database
Created by: mrnugget
This is a little refactoring follow-up to #7328 and changes the UpdateCampaign
code to be a bit more efficient.
If we only need to update the title/description of the existing changesets, we can simply reset the ChangesetJobs in the DB with a single query instead of first loading them into memory and them updating them individually.