(POC) Pin cursors to connections

[prestonvasquez]

The current implementation of MongoBetween uses a cursor caching solution with N >= 1 Mongos (LB7), so cursors being pinned to servers is acceptable. However, when load-balancing at the TCP layer it is not possible to target the same Mongos behind a load balancer when pooling connections (which is done under the hood in the Go Driver). This PR proposes pinning cursors and transactions to connections to account for this.