Include builtin-kas in docker image provided by @kkimurak

I would like to request builtin-kas be added to the image. See the fork provided by @kkimurak

As already reported above (https://github.com/sameersbn/docker-gitlab/pull/2598#issuecomment-1172864976), this image currently does not provides built-in KAS. This PR requires external KAS is exists.

If you have time to do that, could you please try to build and test my support-builtin-kas branch ?
In addition to the work done by @antt1995, I've made sure to build gitlab-kas when building the image and add setting for supervisord to launch kas if enabled. Also I have added configuration file for KAS and minimal configuration parameters.

I have never used Kubernetes so never tested if the registration success, but made sure the gitlab-kas service starts without exiting.
Here are new entries for env of docker-compose.yml on test:

services:
  gitlab:
    environment:
      GITLAB_KAS_ENABLED: 'true'
      # If we don't set this, built-in gitlab-kas will exit with an error
      # See https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/blob/8069d9b79763859b5bcead437a28f4dc73b66ae8/cmd/kas/kasapp/configured_app.go#L96-98
      OWN_PRIVATE_API_URL: grpc://127.0.0.1:8155

Originally posted by @kkimurak in https://github.com/sameersbn/docker-gitlab/issues/2598#issuecomment-1225428725

Start by comparing the support-builtin-kas branch with the current image build, docker-compose.yml environment entries, and the KAS and supervisord configuration it introduces. Build and run the image with GITLAB_KAS_ENABLED=true and OWN_PRIVATE_API_URL=grpc://127.0.0.1:8155; done means the built-in gitlab-kas service starts without exiting and the image includes it.