ashmrtn e15d86e82f
Persist Exchange delta tokens (#1722)
## Description

Begin persisting Exchange delta tokens for data categories that support delta queries. Tokens are stored in a single file as a `map[M365 container ID]token` where both the container ID and token are of type `string`. The file is located in the kopia snapshot that has all the other backup data at the path `tenant-id/{service}Metadata/user/category/delta`. No information about the delta token file is stored in backup details.

## Type of change

- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor

## Issue(s)

* closes #1685 

## Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x]  Unit test
- [ ] 💚 E2E
2022-12-08 18:01:00 +00:00
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2022-11-15 17:34:25 +05:30