Update namespace documentation to reflect new authentication method toggles / gRPC endpoints

[shakeelrao]

Temporal Affiliation

• I am a Temporal employee

Content Suggestion

We recently added a feature that allows namespaces to be mTLS enabled and API key enabled (prior to this, namespaces were "locked" to a single authentication method and couldn't be updated).

We should document the behaviour of toggling an authentication method clearly and have a section describing that if mTLS and API keys are enabled for both namespaces, then there are two different endpoints ones (possibly requiring an update here: https://docs.temporal.io/cloud/namespaces#temporal-cloud-grpc-endpoint).

Note: will add reference links (containing internal information) to the corresponding JIRA ticket.

[fairlydurable]

Thanks for your issue. We'll get that into our system as soon as time allows.