The feature gate gets locked to "true", with the goal to remove it in two
releases.
All code now can assume that the feature is enabled. Tests for "feature
disabled" are no longer needed and get removed.
Some code wasn't using the new helper functions yet. That gets changed while
touching those lines.
Volumes that are provisioned with `VolumeMode: Block` often have a
MetrucsProvider interface declared in their type. However, the
MetricsProvider should implement a GetMetrics() function. In the cases
where the storage drivers do not implement GetMetrics(), a panic can
occur.
Usual type-assertions are not sufficient in this case. All assertions
assume the interface is present. There is no straight forward way to
verify that a valid GetMetrics() function is provided.
By adding SupportsMetrics(), storage driver implementations require
careful reviewing for metrics support.
This PR adds pod-level ephemeral storage metric into Summary API.
Pod-level ephemeral storage usage is the sum of all containers and local
ephemeral volume including EmptyDir (if not backed up by memory or
hugepages), configueMap, and downwardAPI.
For pod volumes that reference a PVC, add a PVCRef to the corresponding
volume stat. This allows metrics to be indexed/queried by PVC name
which is more user-friendly than Pod reference
