[feat gw-api]implement finalizer

[shuqz]

Description

• implement finalizer for target group configuration and load balancer configuration
• LBConfig finalizer will be added during reconcileUpdate and removed during reconcileDelete, it will check both gateway and gatewayClass
• TargetGroupConfig will be added in backend loader and removed when service is deleted

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
  ========== test targetgroupconfiguration =======
  targetgroupconfiguration will be removed when service is deleted
  Test process:

1. targetgroupconfiguration refers to a service
2. http route added this service to trigger reconcile
3. delete service -> finalizer should be deleted
   Result

sic-test-alb % k describe targetgroupconfiguration targetgroupconfiguration-sample -n gateway-alb
Name:         targetgroupconfiguration-sample
Namespace:    gateway-alb
Labels:       <none>
Annotations:  <none>
API Version:  gateway.k8s.aws/v1beta1
Kind:         TargetGroupConfiguration
Metadata:
  Creation Timestamp:  2025-05-30T01:11:34Z
  Finalizers:
    gateway.k8s.aws/targetgroupconfigurations
  Generation:        5
  Resource Version:  21594197
  UID:               582df46b-2d0a-4a41-b23f-ffc42e07bdd0
Spec:
  Default Configuration:
    Health Check Config:
      Health Check Interval:      30
      Health Check Path:          /health
      Health Check Protocol:      http
      Health Check Timeout:       5
      Healthy Threshold Count:    2
      Unhealthy Threshold Count:  2
    Protocol:                     HTTP
    Protocol Version:             HTTP1
    Target Type:                  ip
  Target Reference:
    Group:
    Kind:   Service
    Name:   echoserver2
Events:     <none>

Load balancer Configuration result

k describe loadbalancerconfiguration test-gw-alb-lb-config-1 -n gateway-alb
Name:         test-gw-alb-lb-config-1
Namespace:    gateway-alb
Labels:       <none>
Annotations:  <none>
API Version:  gateway.k8s.aws/v1beta1
Kind:         LoadBalancerConfiguration
Metadata:
  Creation Timestamp:  2025-06-03T20:48:36Z
  Finalizers:
    gateway.k8s.aws/loadbalancerconfigurations
  Generation:        1
  Resource Version:  21606856
  UID:               b2e9ef38-c25d-4625-817d-4f5aa4892990
Spec:
  Load Balancer Name:  customized-alb-lb-name-1
Events:                <none>
$ k delete gateway test-gw-alb -n gateway-alb
gateway.gateway.networking.k8s.io "test-gw-alb" deleted
$ k describe loadbalancerconfiguration test-gw-alb-lb-config-1 -n gateway-alb
Name:         test-gw-alb-lb-config-1
Namespace:    gateway-alb
Labels:       <none>
Annotations:  <none>
API Version:  gateway.k8s.aws/v1beta1
Kind:         LoadBalancerConfiguration
Metadata:
  Creation Timestamp:  2025-06-03T20:48:36Z
  Generation:          1
  Resource Version:    21692623
  UID:                 b2e9ef38-c25d-4625-817d-4f5aa4892990
Spec:
  Load Balancer Name:  customized-alb-lb-name-1
Events:                <none>

• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @shuqz. Thanks for your PR.

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[shraddhabang]

Can we move these adding and removing finalizers methods to FinalizerManager to consolidate them under same manager?

[shuqz]

During offline conversation with Shraddha, she found an edge case when GWA and GWB both refers to GWClass-A. and GWClass A has lbConfig. in this case, when GWA and GWB both got deleted, there is no reconcile to trigger finalizer removal on the remaining gatewayClass based on current logic, will address it

[shraddhabang]

Same lets move this to FinalizerManager