Add the job_variables_attributes as additional parameters to the job …

[tvbeek]

Add the job_variables_attributes as additional parameters to the job play call.

This gives the option to add custom variables to a job.

See: https://docs.gitlab.com/ee/api/jobs.html#run-a-job

I don't know if it is possible to have more validation on the array in the provided options. If that is possible I'm happy to add it.

I didn't see a place with documentation where I need to add something, let me know if I missed it.
If there is anything else that I can/need to change please say it.

[tvbeek]

@GrahamCampbell Small question, do you have any idea when you will have time to look to this PR?

And/or is there something where I can help you with?