Add 'shard' label to 'job_queue_duration_seconds' histogram metric

What does this MR do?

Adds a mechanism to distinguish different kinds of Shared Runners in the CI queue times histogram metric.

Since Runner entity already have a tag concept, we've decided to introduce a specific tag prefix, that will be used to assign metric related shards information.

Because of the possible cardinality of generated Prometheus metrics, we add this mechanism only when the Runner is an instance type (like the existing jobs_running_for_project label). For non-shared runners the shard label will always be set to default.

This is a requirement to handle https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9049.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

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