Merge hub.extraEnv env vars

[danlester]

Merge hub.extraEnv env vars and hub.extraConfig in jupyterhub helm chart.

Changes:

If the following is in the qhub-config.yaml file:

jupyterhub:
  overrides:
    hub:
      config:
        Authenticator:
          enable_auth_state: true
      extraEnv:
      - name: "MYENV1"
        value: "11111"
      - name: "MYENV2"
        value: "22222"

      extraConfig:
        new-config-thing: |
          c.KubeSpawner.something = 123

then, despite the overrides supposed to be added to the JupyterHub Helm release, previously anything under hub.extraEnv would be lost when further overridden by QHub's own required env vars.

This PR merges them instead so the user's env vars should make it into the Hub pod.

Similarly for extraConfig.

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

• Yes
• No

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• No

[viniciusdc]

LGTM! The overrides also affects the jupyterhub.py as well?