feat(discovery): support endpointslices in kubernetes discovery

[dongjiang1989]

Description

This PR add support endpointslices in kubernetes discovery

Checklist

• [x] I have explained the need for this PR and the problem it solves
• [x] I have explained the changes or the new features added to this PR
• [x] I have added tests corresponding to this change
• [x] I have updated the documentation to reflect this change
• [ ] I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[shreemaan-abhishek]

@dongjiang1989 please explain why this is needed, thanks.

[dongjiang1989]

@dongjiang1989 please explain why this is needed, thanks.

@shreemaan-abhishek thanks for your review.

EndpointSlices provide a simple way to track network endpoints within a Kubernetes cluster. They offer a more scalable and extensible alternative to Endpoints.

ref: https://kubernetes.io/docs/concepts/services-networking/endpoint-slices/

[monkeyDluffy6017]

Could you add test cases to cover this?

[dongjiang1989]

@monkeyDluffy6017 @shreemaan-abhishek Please re-check. Thanks

[monkeyDluffy6017]

@zhixiongdu027 Could you help to review this pr?

[AlinsRan]

We should update the documentation for this feature.

[dongjiang1989]

We should update the documentation for this feature.

Thanks. Added it

[dongjiang1989]

/test

[dongjiang1989]

@AlinsRan @shreemaan-abhishek @monkeyDluffy6017 please re-check，thanks