Add ability to complete workflow from any line

[mfateev]

Is your feature request related to a problem? Please describe.
Currently the only way to complete or fail a workflow is through completing (or throwing exception) from the method annotated with @WorkflowMethod. Sometimes it is convinient to complete or fail workflow from some other function or even thread.

Describe the solution you'd like
An API to complete workflow from any place. Strawman:

Workflow.complete(result);
Workflow.fail(Exception); 

Describe alternatives you've considered
Do not introduce this API and rely on completion of main workflow method.l

Additional context
This feature is based on a customer request.

[mfateev]

Similar request: https://community.temporal.io/t/fail-workflow-form-updatemethod/11441