Add activity outcome in start activity response

[ks-temporal]

What changed?

In StartActivityExecution if IncludeOutcome is set in the request and the
activity is already started, and the outcome is available, then instead of
returning AlreadyStarted error, return success with the outcome and runID
of the already started activity.

If the caller desires, it can set the IncludeOutcome in the request, and
the server will return the outcome when the reuse policy is set
to AllowDuplicateFailedOnly and the previous run succeeded,
or when set to RejectDuplicate and the previous run completed.

Before adding the completion callbacks, do the same check, and avoid
adding callbacks on completed activity, as it will fail, but return success
with outcome of the completed activity. Refactor the check-and-add to
a new Activity function to allow unit test.

Why?

So that the outcome is included in response to StartActivityExecution
if the execution is already started, and the activity is already completed,
to avoid another query for the outcome.

When a caller's StartActivityExecution short-circuits to an existing run
with the same activity ID because of an ID reuse or conflict policy, the
caller often wants the outcome of the existing run, not just the identifier
or an error pointing at it. Retrieving the outcome in the response avoids
the caller to use a second RPC of DescribeActivityExecution to retrieve
a result that the server already has cached.

The activity outcome is embedded in a success response rather than
within an error, which otherwise would have happened without the
include_outcome request flag.

How did you test it?

• built
• run locally and tested manually
• covered by existing tests
• added new unit test(s)
• added new functional test(s)

[fretz12]

I think we can simplify

Suggested change

	func (a *Activity) getOutcomeOrAddCallbacks(
	ctx chasm.MutableContext, input getOutcomeOrAddCallbacksInput,
	) (*apiactivitypb.ActivityExecutionOutcome, error) {
	var outcome *apiactivitypb.ActivityExecutionOutcome
	if input.includeOutcome {
	outcome = a.outcome(ctx)
	}
	// Do not add completion callbacks if activity already completed.
	if outcome != nil {
	return outcome, nil
	}
	return nil, a.addCompletionCallbacks(ctx, input.requestID, input.callbacks, input.maxCallbacks)
	}
	func (a *Activity) getOutcomeOrAddCallbacks(
	ctx chasm.MutableContext, input getOutcomeOrAddCallbacksInput,
	) (*apiactivitypb.ActivityExecutionOutcome, error) {
	if input.includeOutcome && a.LifecycleState(ctx).IsClosed() {
	return a.outcome(ctx), nil
	}
	return nil, a.addCompletionCallbacks(ctx, input.requestID, input.callbacks, input.maxCallbacks)
	}