[processor/k8sattributes] Store only necessary data in the pod/replicaset/namespace informers

[dmitryax]

Apply the same optimization as done in SumoLogic/sumologic-otel-collector#593 to all the informers in order to reduce the memory footprint per suggestion from @swiatekm-sumo.

Hopefully, it'll make the heap usage less than before introducing cluster-wise replicaset informers, as reported in #23067.

[swiatekm]

Are we sure we want to do namespaces? Relatively speaking, there tends to be a small number of them in the cluster, and they don't carry a lot of data. Maybe the memory savings aren't worth the additional complexity in their case?

[dmitryax]

Are we sure we want to do namespaces? Relatively speaking, there tends to be a small number of them in the cluster, and they don't carry a lot of data. Maybe the memory savings aren't worth the additional complexity in their case?

I agree. Let's keep the namespaces informer as is.

Closing this issue. Thank you, @swiatekm-sumo!