docs: update plugin examples for ingress controller 2.1.0 release

[kayx23]

Summary

Update plugin docs to match released APISIX Ingress Controller behavior.

Updated in this PR:

• replace stale custom consumer label notes with working Ingress Controller examples in basic-auth, key-auth, jwt-auth, and hmac-auth
• replace stale ApisixConsumer consumer-plugin limitation notes with working APISIX CRD examples in basic-auth, key-auth, jwt-auth, hmac-auth, and limit-count
• update example response snippets to use the namespaced consumer usernames returned by Ingress Controller flows

Validation

• re-verified custom consumer label propagation in APISIX CRD examples
• re-verified consumer-scoped plugin behavior on ApisixConsumer for anonymous-consumer rate-limit flows
• reused the same verified Ingress Controller manifest patterns already checked in the parallel API7/APISIX ingress-controller docs refresh work