feat(chart): add httpRoute.filters for arbitrary filter injection

[tamcore]

Summary

• Adds httpRoute.filters list to values.yaml (default: [])
• When non-empty, filters are injected into the HTTPRoute rule alongside the backendRef
• Generic: works with any Gateway API implementation — not tied to NGF or any specific filter type

Use cases

NGF IP allowlist (whitelist-source-range equivalent):

httpRoute:
  enabled: true
  parentRefs:
    - name: nginx-gateway
      namespace: nginx-gateway
  hostnames:
    - stelloauth.example.com
  filters:
    - type: ExtensionRef
      extensionRef:
        group: gateway.nginx.org
        kind: SnippetsFilter
        name: stelloauth-ip-allowlist

External auth (ExtAuth):

filters:
  - type: ExtensionRef
    extensionRef:
      group: gateway.envoyproxy.io
      kind: HTTPRouteFilter
      name: stelloauth-extauth

Test plan

• httpRoute.filters: [] (default) — renders HTTPRoute with only backendRefs, no filters key
• httpRoute.filters with an ExtensionRef — renders with filters: block in the rule