workload selector should support set-based requirements

[raffaelespazzoli]

(This is used to request new product features, please visit https://discuss.istio.io for questions on using Istio)

Describe the feature request

The type WorkloadSelector, used in many Istio type definitions, and defined here (

api/type/v1beta1/selector.pb.go

Line 32 in 1c84260

type WorkloadSelector struct {

) should align to the kubernetes LabelSelector1, which supports set based requirements.

so it would be possible to not only write expressions like:

 selector:
   matchLabels:
     serving.kubeflow.org/inferenceservice: test-service 

but also expressions like:

        selector:
          matchExpressions:
            - key: "serving.knative.dev/service"
              operator: Exists

Note that this enhancement would 100% back compatible and would like the istio behavior with the more general kubernetes behavior.

Describe alternatives you've considered
There isn't really an alternative for the problem I'm trying to serve.

Affected product area (please put an X in all that apply)

This api type appears in many APIs, not sure which all are, but like I said the change would be backward compatible.

[ ] Configuration Infrastructure
[x] Docs
[ ] Installation
[ ] Networking
[ ] Performance and Scalability
[ ] Policies and Telemetry
[ ] Security
[ ] Test and Release
[ ] User Experience

Additional context

[hzxuzhonghu]

I kind of remember that when workloadSelector was designed, it was for simplicity and it could be easily expanded if further use case is clear.