Add runner type label to queue retrieval duration histogram

What does this MR do?

This merge request adds a runner_type label to the Prometheus histogram we use to record the time it takes to retrieve a builds queue from the database.

We also add this label to the histogram we use to track duration of the entire process of processing a queue for a given runner.

Conformity

• I have not included a changelog entry because it is a backstage improvement.
• Code review guidelines

Issues

See #323967 (closed)