Expose runner names in Prometheus metrics

Description

Currently the only unique identifier exposed by the Prometheus metrics are the first characters of the runner token.

An example: We have a runners manager with 4 auto scaling runner:

• onetime (Token: 12398457)
• multipletimes (Token: 9865374)
• privileged (Token: 89376561)
• onetime-2gitlab (Token: 01856576)

Having only the token available in the Grafana dashboard board makes it unnecessary hard for humans to identify a runner.

Proposal

Expose the runners name in the Prometheus metrics to make it usable in Grafana.

Links to related issues and merge requests / references