`kube_inventory` input plugin: add pod UID to `kubernetes_pod_container`

### Use Case

In some cases, subsequent pods have the same name (e.g. when pods are only by a StatefulSet).
In these cases, the `kubernetes_pod_container` metric cannot indicate which one of the pods it is, as there's only a `pod_name` tag and no `pod_uid` tag.

### Expected behavior

Provide a `pod_uid` tag in `kubernetes_pod_container` metric.

### Actual behavior

No `pod_uid` tag.

### Additional info

Briefly looking at the plugin's code, it seems quite easy to do, so I'm willing to submit a PR for that if you accept the suggestion.

Start by locating the kube_inventory input plugin and the code that assembles the kubernetes_pod_container metric tags. Trace the pod metadata available there, then update the relevant metric coverage so the pod_uid tag is present and verify the plugin tests or metric output confirm it.

Written by the indexing model from the issue text.