adds a tombstone collection for any drive that has been completely deleted (or that surfaced from a prior backup, but does not exist in the current) from the driveish account.
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#### Does this PR need a docs update or release note?
- [x] ✅ Yes, it's included
#### Type of change
- [x] 🐛 Bugfix
#### Issue(s)
* #3379
#### Test Plan
- [x] ⚡ Unit test