Forward entrypoint logs

What does this MR do?

For the k8s executor: forwards logs emitted by the container's entrypoint from the k8s api to the build logger, iff FF_KUBERNETES_HONOR_ENTRYPOINT is set.

Why was this MR needed?

To make sure, users see all logs they'd expect and to reach parity with the docker executor.

What's the best way to test this MR?

go test -count=1 -tags=kubernetes,integration -v -run '(?i).*entry.*' ./executors/kubernetes/
go test -count=1 -v -run '(?i).*entry.*' ./executors/kubernetes/

Use

• this config.toml

  listen_address = ":9252"
  concurrent = 1
  check_interval = 1
  log_level = "debug"
  connection_max_age = "15m0s"
  shutdown_timeout = 0
  
  [session_server]
    session_timeout = 1800
  
  [[runners]]
    name = "hhoerl-gitlab"
    url = "https://gitlab.com"
    id = 40502329
    token = "glrt-NOPENOPENOPE"
    token_obtained_at = 2024-08-09T13:39:07Z
    token_expires_at = 0001-01-01T00:00:00Z
    executor = "kubernetes"
    shell = "bash"
    [runners.kubernetes]
      host = ""
      image = "alpine"

• and thisgitlab-ci.yaml

  stages:
    - test
  
  test:
    variables:
      CI_DEBUG_SERVICES: true
      FF_SCRIPT_SECTIONS: true
      FF_PRINT_POD_EVENTS: true
      FF_RETRIEVE_POD_WARNING_EVENTS: true
      FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY: false   ## <- toggle this
      FF_KUBERNETES_HONOR_ENTRYPOINT: true  ## <- toggle this 
    stage: test
    services:
      - name: postgres:11.6
    image:
      name: registry.gitlab.com/gitlab-org/gitlab-runner/alpine-entrypoint-pre-post-trap
      # name: registry.gitlab.com/gitlab-org/gitlab-runner/powershell-entrypoint-pre-post-trap
    script:
      - echo "hello world"

against a GitLab instance and see

• the job succeed
• the job log shows the entrypoint logs

What are the relevant issue numbers?

closes: #37468 (closed)