seems like a lot of code, but this is 95% boilerplate additions copied from groups collections packages, with a find-replace for names.
Some noteworthy differences:
* teamsChats does not handle metadata, so all metadata, delta, and previous path handling was removed
* teamsChats does not produce tombstones
* chats are never deleted, so no "removed" items are tracked
* all chats gets stored at the prefix root, so no "containers" are iterated, and therefore only one collection is ever produced.
This means that, overall, while the boilerplate here is still the same, it's much reduced compared to similar packages.
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#### Does this PR need a docs update or release note?
- [x] ⛔ No
#### Type of change
- [x] 🌻 Feature
#### Issue(s)
* #5062
#### Test Plan
- [x] ⚡ Unit test
- [x] 💚 E2E
