Fix hostname override and type for status_report.count metrics

[xvello]

What does this PR do?

The hostname of the .container.status_report.count.waiting and .container.status_report.count.terminated metrics was not extracted from the label join map.

Add the OpenMetricsScraperMixin.get_hostname_for_sample public method to expose the information to checks, and use it for these two metrics.

Also, set the metric type as gauge, as count bring erroneous values (counted by the app as the number of count calls per minutes, instead of per check run). As the timeseries are container cardinality (pod and kube_container_name tags), no client-side aggregation is needed for gauges.

Motivation

What inspired you to submit this pull request?

Review checklist

• PR has a meaningful title or PR has the no-changelog label attached
• Feature or bugfix has tests
• Git history is clean
• If PR impacts documentation, docs team has been notified or an issue has been opened on the documentation repo

Additional Notes

Anything else we should know when reviewing?