Allow consumption of Change Feed as a in-memory push model in SDKv3
Unlike the older SDK, the SDKv3 doesn't support the InMemory Lease Container yet. But this is very useful e.g. if you just want to use the ChangeFeed to keep your local caches up2date.
This is also described here: https://github.com/Azure/azure-cosmos-dotnet-v3/issues/972
This is now complete.
Merged PR is here.