Cherry-pick #16554 to 7.x: Fix k8s pod annotations tier in metadata

[ChrsMark]

Cherry-pick of PR #16554 to 7.x branch. Original message:

Follow-up of #16480 PR.

It was found also that kubernetes.annotations.* do not follow the schema defined at

beats/libbeat/processors/add_kubernetes_metadata/_meta/fields.yml

Line 38 in 2e4d292

- name: annotations.*

any more.

This PR aims to fix it.

Not sure if we should fix it in general for all resources at

beats/libbeat/common/kubernetes/metadata/resource.go

Line 105 in dba8f74

safemapstr.Put(meta, strings.ToLower(kind)+".annotations", annotationsMap)

and not only for pods. I think we should do it sooner or later when we define a general strategy about this schema as mentioned #16480 (comment).