Columnar: open cluster connection in background

In order to support the upcoming columnar SDKs, the C++ core should have a mechanism to allow bootstrap to occur in the background.

Key points for this feature:

• connect in the background

• track topology on the cluster level

  • Currently the C++ client only tracks topology on the bucket level

• Continuous retry on bootstrap failure until success or user disposes of the cluster instance

• Mechanism for http_session_manager to subscribe to bootstrap failures so that http request can fast-fail in certain scenarios (e.g. prior to the initial bootstrap success)