Add support for adding custom labels and environment variables to nodes via spec

[jlamillan]

Greetings!

This pull-request resolves #135 by adding support add custom labels and environment variables to nodes via spec, which get propagated to the node deployments/pods.

  nodePools:
    - component: nodes
      ...
      labels:
         myLabel: foo
         anotherLabel: bar
      env:
        - name: qux
          value: "quux"
        - name: quuz
          valueFrom:
            configMapKeyRef:
              name: quuz-configmap
              key: corge

[jlamillan]

I also added test coverage for user defined labels and env vars.

[swoehrl-mw]

Two comments from my side:

• I would prefer the field to be named just env instead of envVars, that way we would be consistent with kubernetes naming
• We should consider making it more generic so that users can specify the same things as they can in a pod spec (so not just value but also valueFrom)

[jlamillan]

Two comments from my side:

* I would prefer the field to be named just `env` instead of `envVars`, that way we would be consistent with kubernetes naming

* We should consider making it more generic so that users can specify the same things as they can in a pod spec (so not just value but also valueFrom)

Sounds good. I've made these changes and squashed the commits.

[swoehrl-mw]

LGTM. If you could work in the complaint from the linter, I'll approve the PR.

[jlamillan]

LGTM. If you could work in the complaint from the linter, I'll approve the PR.

All set.

[swoehrl-mw]

@jlamillan Merged. Thank you for your work with this PR. Much appreciated.