Missing docs about MeshSubset and MeshServiceSubset

[schogges]

Description

In the docs there are many occurrences of MeshSubset and MeshServiceSubset, but I could not find a dedicate documentation about these resources. In the code I could find something in the app/_posts/2022-12-20-policy.md.

MeshSubset: a subset of dataplane proxies across all services that have a set of tags

targetRef:
 kind: MeshSubset
 tags:
   k8s.kuma.io/namespace: ns-1

MeshServiceSubset: Like MeshService with extra tags to select a subset of all dataplanes. For example you could pick only dataplanes with the tag version: v2.

targetRef:
 kind: MeshServiceSubset
 name: backend_ns1_svc_80
 tags:
   version: v2

[michaelbeaumont]

We talk about them in the policy introduction but part of the problem is probably that this is impossible to find by searching

[lobkovilya]

Triage: we should make sure targetRef kinds explained here https://kuma.io/docs/2.9.x/policies/introduction/#writing-a-targetref pop up in the search.