Set variables on Fail Job via Go client

[korthout]

Is your feature request related to a problem? Please describe.
Recently, we introduced the ability to set variables when failing a job to Zeebe. The FailJob RPC now supports passing these variables along. Additionally, the zeebe-java-client now provides an interface to pass variables along when failing a job, but the Go client was left out of scope.

• I can set variables when failing a job #9404

Describe the solution you'd like
Add a way to pass variables along when failing a job via the Go client. Inspiration can be taken from other RPCs that support passing variables along like CompleteJob.

Describe alternatives you've considered
It's possible to add this support to zbctl once it's implemented in the Go client, but I don't see a need for it now. We can implement this in a separate issue if/when users ask for it.

Additional context
This functionality was implemented for the Java client in:

• feat(client-java): support set variables when failing a job #10705