Enable runner for minikube

Enables GitLab Runner for Minikube since !1360 (merged) enabled automatic generation of the certificate chain.

Testing

Instructions

1. minikube start --cpus 3 --memory 8192 --kubernetes-version=1.18.3 --driver=virtualbox
2. helm upgrade --install gitlab gitlab/gitlab --timeout 600s -f examples/values-minikube-minimal.yaml --set global.hosts.domain=$(minikube ip).nip.io --set global.hosts.externalIP=$(minikube ip)
3. Confirm runner is connected
4. Create project with pipeline

Runner connected automatically

gitlab-gitlab-runner Registering runner... succeeded                     runner=jiip6ax5                                                                                                                                                                 │
│ gitlab-gitlab-runner Runner registered successfully. Feel free to start it, but if it's running already the config should be automatically reloaded!                                                                                                     │
│ gitlab-gitlab-runner Runtime platform                                    arch=amd64 os=linux pid=1 revision=6fbc7474 version=13.1.1

Successful pipeline with Runner