Docker must be installed on runner

[turbo-badex]

For experienced DevOps, it might seem obvious but for beginners, I think it's important to state that the AWS instance for the runner should have docker installed. The build will fail if docker isn't installed.

Also, some variables declared in the docker file needs to be declared inside gitlab in the variables subsection under CI/CD settings.

After installing docker on the instance, to avoid any permission issues from the runner trying to connect to the Docker daemon socket, I highly recommend adding the GitLab CI User to the Docker Group using the command:
sudo usermod -aG docker gitlab-runner