Extend WorkflowImplementationOptions with ChildWorkflowOptions

[porunov]

Currently, when building WorkflowImplementationOptions it is possible to set ActivityOptions, LocalActivityOptions, and NexusServiceOptions.
It would be great if there was a method to set ChildWorkflowOptions in the same way using the methods:

• setChildWorkflowOptions(Map<String, ChildWorkflowOptions> options)
• setDefaultChildWorkflowOptions(ChildWorkflowOptions options)

[tconley1428]

Seems like a reasonable request. We'll triage and see what we can do.