CosmosDb provider doesn't support a configuration option for a current region

[dimangulov]

It is an enhancement. Right now, EF Core for CosmosDb doesn't have an option to specify what a region should be used to connect to.

That is why I cannot use the CosmosDb's global distribution feature.
More details can be found, here:
https://docs.microsoft.com/bs-latn-ba/azure/cosmos-db/tutorial-global-distribution-sql-api?view=cntk-py-2.3

I will create a pull request