[k8s] Consider `k8s.container.instance` entity

[ChrsMark]

Chatted a bit about this with @dmitryax during last K8s SIG meeting.
Probably what we will need for "capturing" the k8s container's restarts/instances is sth like a k8s.container.instance entity similar to

semantic-conventions/model/service/entities.yaml

Lines 18 to 31 in fd1fb75

	- id: entity.service.instance
	type: entity
	name: service.instance
	brief: >
	A unique instance of a logical service.
	note: >
	A `service.instance` uniquely identifies an instance of a logical service. For example,
	a container that is part of a Kubernetes deployment
	that offers a service.
	stability: development
	attributes:
	- ref: service.instance.id
	role: identifying
	requirement_level: required

. However for k8s.container entity the k8s.container.restart_count is just a descriptive attribute.

Originally posted by @ChrsMark in #3135 (comment)

Specifically this would be used for container's logs at https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/stanza/docs/operators/container.md#add-metadata-from-file-path.