[Prioritized] Hourly Cleanup/Backup Job for `azure-sdk-assets`

This job should run in two steps primarily.

- [x] Scan. Discover all the pointers FROM assets.jsons existing in commits in each language repo.
- [ ] Backup. Wes suggested pushing any new tags to a forked Azure-sdk-assets repo. Specifically, `azure-sdk`'s fork.
- [ ] Extend `mirror` job logic to also handle tags if told to
- [ ] Fork azure-sdk-assets using `azure-sdk`
- [ ] Setup mirror job from `Azure/azure-sdk-assets` -> `azure-sdk/azure-sdk-assets`
- [ ] Cleanup any tags _created more than a month ago_ that do not exist in a main repo commit.
- [ ] Backup should allow configuration of patterns of tags that are _never_ cleaned up.