feat: add secret/service resource checker for webhook

[ronething]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches
• Documentation
• Refactor
• Chore
• CI/CD or Tests

What this PR does / why we need it:

• Implement GatewayProxy admission webhook warnings for missing Service/Secret references.
• Implement ApisixConsumer admission webhook warnings for missing Secret references.
• Implement ApisixTls admission webhook warnings for missing Secret references.
• Implement ApisixRoute admission webhook warnings for missing Service/Secret references.
• Implement Consumer (v1alpha1) admission webhook warnings for missing Secret references.

Currently, resources such as GRPCRoute and HTTPRoute are still missing, and they will be handled in the next PR.
Then the logic of Ingress webhook and Gateway webhook needs to be expanded, and there is currently no support for checking missing Secret/Service.
Additionally, the current supplement is unit tests, while e2e tests have not been added yet. But these unit tests should be sufficient for this PR.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[Copilot]

Pull Request Overview

This PR implements admission webhook validation for multiple APISIX resources to check for missing Service and Secret references. The validation provides warnings to users when referenced resources don't exist in the cluster, improving user experience and catching configuration errors early.

Key changes:

• Added a reusable reference checker utility for Service and Secret validation
• Implemented webhooks for GatewayProxy, ApisixConsumer, ApisixTls, ApisixRoute, and Consumer resources
• Added comprehensive unit tests for all webhook validators

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/e2e/scaffold/grpc.go	Minor import reorganization for better code formatting
internal/webhook/v1/reference/checker.go	Core utility for validating Service and Secret references with admission warnings
internal/webhook/v1/*_webhook.go	Webhook validators for GatewayProxy, Consumer, ApisixTls, ApisixRoute, and ApisixConsumer
internal/webhook/v1/*_webhook_test.go	Comprehensive unit tests for all webhook validators
internal/manager/webhooks.go	Registration of new webhooks with the manager
config/webhook/manifests.yaml	Webhook configuration manifests for Kubernetes admission controllers

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