Add type safe API to execute an async update workflow request

[Quinn-With-Two-Ns]

Add type safe API to execute an async update workflow request.

Open questions we should resolve:

1. Is the name executeUpdate acceptable? We could also use update or startUpdate the Java SDK is not very consistent here
2. Is taking UpdateOptions OK or do we want a new type here? Reusing is nice since it reduces the number of types, but has some redundant fields like name, and type.

closes #2181

[Quinn-With-Two-Ns]

@dandavison FYI The naming of this API may be relevant to your work on update with start

[dandavison]

Is the name executeUpdate acceptable? We could also use update or startUpdate the Java SDK is not very consistent here

The only place that the Java SDK uses "execute" AFAIK is WorkflowClient.execute which returns a (future of) workflow result. So across all SDKs, we have a pattern that "execute" always means "returning result, not run/handle" (with the exception of Go's ExecuteWorkflow which is a clear outlier -- if we were naming that nowadays we'd call it StartWorkflow.) So that argues that, since the new methods added here return WorkflowUpdateHandle, they should not have "execute" in their name.

So startUpdate seems best here, since in Java we have the pattern untypedStub.startUpdate => UpdateHandle and untypedStub.update => UpdateResult.

[cretz]

No comment on update options

[cretz]

IMO this should be called startUpdate even though I know Java is not that consistent here. I think it's clearer to understand and allows us to offer a real executeUpdate later if we wanted. I'd also support update.

[Quinn-With-Two-Ns]

Yep seems there is consensus that we should call this startUpdate so I renamed it.