[Cosmos] Fix retry handling for Session Not Found errors

[southpolesteve]

In high throughput scenarios with multiple regions, replication lag can sometimes cause a session to not be available. A client will write a document to Region A, and later attempt to read it from Region B. But the session token from region A has not yet been replicated to Region B. This results in Error 404, substatus 1002: Session Not Found.

In these cases the SDK is supposed to retry the request on other regions and if still unsuccessful retry the request again with no session token establishing a new session token. This code was not working correctly. This PR fixes the logic and and adds a test that simulates an out of date session token in a single region scenario.

1. Add session token test simulating 404/1002 condition
2. Properly increment retryCount
3. Instantiate retryCount to 0. Previously it was undefined. var++ for undefined == NaN
4. Remove session token header when request is being retried

[southpolesteve]

Closed in favor of #17034