Add test for permissions container in k8s

What does this MR do?

Add test for permissions container in k8s

Why was this MR needed?

In !2578 (merged) we are fixing a bug where users will be able to use the helper image when overridden. Add tests to validate that this works and to make sure we don't break it in the future.

What's the best way to test this MR?

1. Run the test go test -v -run TestExecutor_buildLogPermissionsInitContainer ./executors/kubernetes/...

If you want to check if all of the feature is working, run the following

1. Update config.toml to have the following

   config.toml

   [[runners]]
     name = "kubernetes"
     url = "http://gdk.test:3000/"
     token = ""
     executor = "kubernetes"
     environment = ["FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY=false"]
     [runners.kubernetes]
       bearer_token_overwrite_allowed = false
       image = "alpine:3.12"
       privileged = true
       helper_image = "public.ecr.aws/gitlab/gitlab-runner-helper:x86_64-latest"

2. Run job like the following:

   .gitlab-ci.yml

       job:
     stage: test
     script:
       - sleep 60

3. Check that initContainer is using the helper image override

   shell

   $ kubectl get po
   NAME                                           READY   STATUS            RESTARTS   AGE
   runner-mkp1g3gh-project-20-concurrent-0tnmrh   0/2     PodInitializing   0          2s
   
   $ kubectl get po/runner-mkp1g3gh-project-20-concurrent-0tnmrh  -o json  | jq '.spec.initContainers | keys[] as $k | "\\(.[$k] | .image)"'
   "public.ecr.aws/gitlab/gitlab-runner-helper:x86_64-latest"

What are the relevant issue numbers?

Closes #27393 (closed)