Add k8s Pod volume metrics

[ChrsMark]

Fixes #1485

Changes

This PR adds k8s.pod.volume.* metrics:

k8s.pod.volume.available
k8s.pod.volume.capacity
k8s.pod.volume.usage
k8s.pod.volume.inode.count
k8s.pod.volume.inode.used # This may not be equal to `inode.count - inode.free` because filesystem may share inodes with other filesystems.
k8s.pod.volume.inode.free

Collector ref: https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/v0.127.0/receiver/kubeletstatsreceiver/documentation.md#k8svolumeavailable
Collector implementation: https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/v0.127.0/receiver/kubeletstatsreceiver/internal/kubelet/volume.go#L16

These metrics are derived from the VolumeStats field of the PodStats of the Kubelet's stats API.

Note: The current implementation reports them as k8s.volume.* but I think they should be k8s.pod.volume.* to better indicate the scope since there is no concept a K8s Volume outside of the Pod context.

Attributes for volume types that are deprecated are not added here: open-telemetry/opentelemetry-collector-contrib#40477

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[dashpole]

Do you think it would make sense to consistently use used vs capacity everywhere, and omit free/available?

[ChrsMark]

Do you think it would make sense to consistently use used vs capacity everywhere, and omit free/available?

If I understand the suggestion correctly, it seems that free/available would still be useful/needed?

From https://pkg.go.dev/k8s.io/kubelet@v0.33.0/pkg/apis/stats/v1alpha1#FsStats:

• UsedBytes: This may differ from the total bytes used on the filesystem and may not equal CapacityBytes - AvailableBytes.
• InodesUsed : This may not equal Inodes - InodesFree because this filesystem may share inodes with other "filesystems"

[dashpole]

ah, right

[ChrsMark]

However, based on this I think it makes sense to record also the UsedBytes as well. I will update the PR to add this.

[odubajDT]

Would it be possible to add a k8s.volume.usedmetric? Details here open-telemetry/opentelemetry-collector-contrib#40476

[ChrsMark]

Would it be possible to add a k8s.volume.usedmetric? Details here open-telemetry/opentelemetry-collector-contrib#40476

It's done: 5459577

[ChrsMark]

@dashpole your comments should be addressed now, please take another look when you get the chance.

[ChrsMark]

@open-telemetry/specs-semconv-approvers @open-telemetry/specs-semconv-maintainers please take a look