Figure out agent_plan_content backups
We're storing work plans (variously: agent plans, work item agent plans, workplans, ...?) in object storage, per:
* https://gitlab.com/gitlab-org/gitlab/-/merge_requests/232335+
* https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/9382+
* https://gitlab.com/gitlab-org/charts/gitlab/-/merge_requests/5029+
There is a whole situation with having these backed up correctly, per [this thread](https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/9382#note_3337992805) and `@ibaum`'s comment at the end:
> So I think it will just require a rails issue, and a CNG/charts issue to add backup support.
Figure out how this works end-to-end and correct.
issue