Update ReplicaSet concept topic

[steveperry-53]

This is a...

• [ x] Feature Request
• Bug Report

Proposed Solution:
Update the ReplicaSets concept topic.

• Remove time-sensitive phrases like "is the next-generation".
• Bring text and code examples into alignment with our style guide.
• Add an explanation of how a Pod has an ownerReference, and a ReplicaSet can be the owner of a
  Pod.
• Explain in detail how the ReplicaSet controller bases its actions on both Pod labels and Pod
  ownerReference.
• Possibly simplify code examples. For example, why does the main example have both matchLabels
  and matchExpressions?

selector:
    matchLabels:
      tier: frontend
    matchExpressions:
      - {key: tier, operator: In, values: [frontend]}

Page to Update:
https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/#pod-selector

[steveperry-53]

Contacts: @chenopis, @steveperry-53

[zacharysarah]

/cc @juandiegopalominocardich

[juandiegopalomino]

👍

[bradtopol]

@steveperry-53 @zacharysarah I assigned myself this topic and should be able to start it next week. I'm at a conference this week. If someone can work on it sooner let me know and I will unassign myself.

[zacharysarah]

@bradtopol Thanks, I think @juandiegopalomino has a PR well in progress already.

JD, would you please edit your PR’s original description to include the following on a single line:
fixes #12081
Thanks!

[juandiegopalomino]

@zacharysarah done, and my pr is already merged

[DanyC97]

so i guess this issue is fixed hence can be closed now that 12409 is merged ?

[juandiegopalomino]

I guess so?

[DanyC97]

@steveperry-53 you agree? if so you mind closing the issue ?