Add, parse, and configure info about retention
when initializing a repo. These flags are
currently marked as hidden
Medium-term, they can be used in longevity
tests when making the repo for the first time
(we can configure this out of band if needed
though)
Long-term, they can be exposed to the user
for immutable backup support
---
#### Does this PR need a docs update or release note?
- [ ] ✅ Yes, it's included
- [x] 🕐 Yes, but in a later PR
- [ ] ⛔ No
#### Type of change
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [x] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup
#### Issue(s)
* #3799
#### Test Plan
- [x] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E
