feat: Allow awaiting job.stop() (#977)

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## Description

I believe this would be useful for building a job manager (see:
#871)
and supporting graceful shutdown (see:
#713).

## Related Issue

#976 

## Motivation and Context

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- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

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Co-authored-by: Brandon der Blätter <intcreator@users.noreply.github.com>

Author: ehooi

src/job.ts

@@ -354,7 +354,7 @@ export class CronJob<OC extends CronOnCompleteCommand | null = null, C = null> {
 			return;
 		}
 
-		void Promise.resolve().then(async () => {
+		return Promise.resolve().then(async () => {
 			await this._waitForJobCompletion();
 			await this._executeOnComplete();
 		});