Allow SDKs to support connecting to multiple endpoints for Multi-region Namespaces

[atihkin]

Is your feature request related to a problem? Please describe.

Temporal Cloud customers (specifically those with more complicated network setups using Private Connectivity) encounter issues due to misconfigured Workers when a Namspace is failed over to a standby region in the event of an incident. To improve this user experience, we should consider switching to a per region end point and change our SDKs to natively handle failovers (instead of relying on manual user setup).

Describe the solution you'd like

There are three requirements in this task:

1. Allow SDK to be able to connect to multiple endpoints for a namespace. Typical use case is region specific endpoints for MRN, and different endpoints for on-prem to cloud migration.
2. SDK should send requests to the “active“ endpoint based on the ns info it gets from Temporal server.
3. SDK should health check both endpoints to prevent connection errors post namespace failover.

Per-SDK Tickets

TBA