docs: fix generated CRD reference self-links

[kayx23]

Summary

• map external Gateway API aliases and time.Duration to their authoritative references
• omit Appears in links for types excluded from the generated document
• add a generated CRD self-link checker to the Makefile and CI
• regenerate the CRD API reference

Why

crd-ref-docs treated four Gateway API aliases and time.Duration as locally rendered types, producing links to headings that do not exist. The template also linked to ConsumerStatus even though that type is excluded from the output. These six broken fragments were copied into downstream documentation whenever the reference was regenerated.

Validation

• confirmed the checker fails on the previous output with exactly six missing fragments
• regenerated the reference twice and confirmed byte-identical output
• checked 229 generated self-links against 102 Docusaurus heading IDs; all resolve
• confirmed all five external pkg.go.dev anchors return HTTP 200
• make check-crd-doc-links
• git diff --check
• Python syntax check for scripts/check-crd-doc-links.py

This is the Apache APISIX Ingress Controller counterpart to api7/api7-ingress-controller#494.