Improve runner_name metric label coverage

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What does this MR do?

Adds runner name label to several prometheus metrics

• gitlab_runner_jobs
• gitlab_runner_jobs_total
• gitlab_runner_failed_jobs_total
• gitlab_runner_job_duration_seconds
• gitlab_runner_job_queue_duration_seconds
• gitlab_runner_job_stage_duration_seconds
• gitlab_runner_acceptable_job_queuing_duration_exceeded_total
• gitlab_runner_limit

Why was this MR needed?

Runner short description isn't helpful to humans when building dashboards, in multi runner setups this makes visualizing these metrics much more useful.

What's the best way to test this MR?

make test or launch gitlab-runner and verify metrics are available with expected runner_name label over metrics endpoint.

What are the relevant issue numbers?

#26660 (closed)