[Feature Request] SDKs should differentiate between `NamespaceInvalidState` and `NamespaceNotFound` errors

[bergundy]

More info in these PRs:

• https://github.com/temporalio/temporal/pull/2785
• https://github.com/temporalio/api/pull/179

Checklist:

• [x] Go - https://github.com/temporalio/sdk-go/pull/799 + https://github.com/temporalio/sdk-go/pull/801
• [ ] Java
• [ ] Core
• [ ] TS
• [ ] PHP
• [ ] .NET

[cretz]

And specifically, the worker should consider NamespaceNotFound error a fatal error, but not NamespaceInvalidState.