Add high-level workflow describe

[Quinn-With-Two-Ns]

closes #2265

[cretz]

Can we make this constructor package private like its super class? I assume this is public because it is interceptable? Not sure the describe call needs to be interceptable if the list call isn't. Or if we want to make the list call interceptable, we can and then expose the constructor of WorkflowExecutionMetadata.

[Quinn-With-Two-Ns]

Yes it is public because it is intercept-able, It was a requirement on the issue. The list call is not intercept-able right now but it makes sense to open an issue to add that as well and expose the constructor of WorkflowExecutionMetadata, but I would prefer to do that in a separate issue.

[Quinn-With-Two-Ns]

Opened an issue to track making list intercept-able #2328