feat: add extra config to deployment

In this MR I added 2 new config parameters: templateSpecOverride and containerOverride, which can be used to add something like volume to a deployment.

I need to add a configmap or a secret as a file (for example, a project using google cloud GOOGLE_APPLICATION_CREDENTIALS), which is not possible with the default chart.

example using extra.spec

containerOverride:
  volumeMounts:
  - name: sample-volume
    readOnly: true
    mountPath: "/etc/sample_config"
templateSpecOverride:
  volumes:
    - name: sample-volume
      secret:
        secretName: sample-config-map

The extra config comes last so it will override any existing field.