Add support for specify ConfigMaps for gitlab-runner deployment

What does this MR do?

Allows the user to set any configmap he needs to be mounted inside the runner container

Why was this MR needed?

Need to add a configuration file for the autoscaler custom executor driver

What's the best way to test this MR?

Add to your values.yaml

configmaps:
  foo: |
    echo "foo"

helm template test . should show the config map being added

# Source: gitlab-runner/templates/configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: test-gitlab-runner
  labels:
    app: test-gitlab-runner
    chart: gitlab-runner-0.27.0-beta
    release: "test"
    heritage: "Helm"
data:
  
  ...

  pre-entrypoint-script: |
    

  foo: |
    echo "foo"

What are the relevant issue numbers?

gitlab-org/ci-cd/custom-executor-drivers/autoscaler#65 (closed)