feat(api-clients/grpc): add variables argument for FailJob gRPC

[skayliu]

What is the purpose of the change

Add variables argument for FailJob gRPC.

closes #1387

Are there related marketing activities

No.

When should this change go live?

May be C8.2.

PR Checklist

• My changes apply to an already released version, and I have added them to the relevant /versioned_docs directory, or they are not for an already released version.
• My changes apply to future versions, and I have added them to the main /docs directory, or they are not for future versions.
• My changes require an Engineering review, and I've assigned an engineering manager or tech lead as a reviewer, or my changes do not require an Engineering review.
• My changes require a technical writer review, and I've assigned @christinaausley as a reviewer, or my changes do not require a technical writer review.

[skayliu]

Hi, @korthout, I've updated the doc, Please review this, Thank you.

[korthout]

Thanks @skayliu ❤️ , I'll have a look at this in the coming days.

[korthout]

Thanks @skayliu 🚀

This change made me wonder whether we also need to update:

• https://docs.camunda.io/docs/next/components/concepts/job-workers/#completing-or-failing-jobs

❓ But I'm not sure, because that page explains the basic job worker concept while this feature is for rather advanced use cases. I'd be curious to hear your opinion about this.

🔧 Please consider my suggestion

[skayliu]

• https://docs.camunda.io/docs/next/components/concepts/job-workers/#completing-or-failing-jobs

@korthout what you think add these?

When Completing or failing jobs with variables, the variables are merged into the process of the job's associated task.

• If Completing a job the variables are propagated from the scope of the task to its higher scopes.
• If Failing a job the variables are only created in the local scope of the task.

[christinaausley]

No adjustments from a technical writing perspective on this one 👍

[korthout]

Thanks for the additional changes @skayliu

@christinaausley Let me know what you think about linking ahead in the concepts and about my grammar suggestion.

[korthout]

LGTM 🏅