fix: setup indexer should consider api support or not

[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:

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 fixes the indexer setup to conditionally configure Gateway API indexers based on whether the corresponding APIs are available in the cluster, preventing failures when Gateway API CRDs are not installed.

• Adds conditional setup logic using utils.HasAPIResource() to check API availability before configuring indexers
• Separates Gateway API indexers from core Kubernetes/APISIX indexers
• Adds logging to indicate when indexers are skipped due to missing APIs

[github-actions]

conformance test report - apisix-standalone mode

apiVersion: gateway.networking.k8s.io/v1
date: "2025-07-31T04:01:10Z"
gatewayAPIChannel: standard
gatewayAPIVersion: v1.2.0
implementation:
  contact: null
  organization: APISIX
  project: apisix-ingress-controller
  url: https://github.com/apache/apisix-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    result: partial
    skippedTests:
    - HTTPRouteHTTPSListener
    statistics:
      Failed: 0
      Passed: 32
      Skipped: 1
  name: GATEWAY-HTTP
  summary: Core tests partially succeeded with 1 test skips.

[github-actions]

conformance test report - apisix mode

apiVersion: gateway.networking.k8s.io/v1
date: "2025-07-31T04:01:57Z"
gatewayAPIChannel: standard
gatewayAPIVersion: v1.2.0
implementation:
  contact: null
  organization: APISIX
  project: apisix-ingress-controller
  url: https://github.com/apache/apisix-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    failedTests:
    - HTTPRouteMatchingAcrossRoutes
    result: failure
    skippedTests:
    - HTTPRouteHTTPSListener
    statistics:
      Failed: 1
      Passed: 31
      Skipped: 1
  name: GATEWAY-HTTP
  summary: Core tests failed with 1 test failures.

[github-actions]

conformance test report

apiVersion: gateway.networking.k8s.io/v1
date: "2025-07-31T04:07:11Z"
gatewayAPIChannel: standard
gatewayAPIVersion: v1.2.0
implementation:
  contact: null
  organization: APISIX
  project: apisix-ingress-controller
  url: https://github.com/apache/apisix-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    result: partial
    skippedTests:
    - HTTPRouteHTTPSListener
    statistics:
      Failed: 0
      Passed: 32
      Skipped: 1
  name: GATEWAY-HTTP
  summary: Core tests partially succeeded with 1 test skips.