SDK API for describing workflow

[cretz]

Describe the solution you'd like

• SDKs should make describing a workflow easy
• Ideally, the response is a language-idiomatic wrapper that [at least] exposes a shortcut for status and provides access to the underlying DescribeWorkflowExecutionResponse
• Do we want a different name other than describe?
• Should existing SDKs w/ their own describe calls already in use still create this wrapper?

[Sushisource]

We might consider making this more generally about "wrap grpc call responses in types that expose the raw message but also provide higher-level helpers"

[cretz]

Describe is the only call I think that applies to across all SDKs atm. Granted it applies for errors and such too. But I don't think any other calls we generally wrap are complex enough to need raw protos yet.