Update GitLab CI docs: Add --tls=false to docker-in-docker to avoid startup delays

[ulrichwinter]

Starting the docker:dind service in GitLab CI without --tls=false leads to the following warning within the docker sidecar container:

Binding to an IP address without --tlsverify is deprecated. Startup is intentionally being slowed down to show this message

If a gitlab-ci build job accesses the docker api right at the start, the job might fail.

This behaviour has been observed with docker 20.10.9 and a kubernetes-executor for the gitlab-runner.
It can be reproduced with the pipeline job below, but the public gitlab runner from gitlab.com is not affected by this behaviour.

Therefore I suggest to provide a hint to this --tls=false argument within the testcontainer docs.

# DinD service is required for Testcontainers
services:
  - docker:dind

variables:
  # Instruct Testcontainers to use the daemon of DinD.
  DOCKER_HOST: "tcp://docker:2375"
  # Instruct Docker not to start over TLS.
  DOCKER_TLS_CERTDIR: ""
  # Improve performance with overlayfs.
  DOCKER_DRIVER: overlay2

test:
  image: docker:20.10.9
  stage: test
  script:
    - docker info

[kiview]

Hi @ulrichwinter,
thanks a lot for this very helpful hint and corresponding doc update, LGTM 👍

[bsideup]

Nice! 👍

[ulrichwinter]

That was quick.
Thanks a lot for the support.