Allow extraEnvVars that use valueFrom

[ejstreet]

Describe the problem/challenge you have
The chart as it is currently configured does not allow passing extraEnvVars that use a valueFrom, it enforces name and value inputs only using a range.

Describe the solution you'd like
Allow the extraEnvVars to support all valid env inputs e.g.

extraEnvVars:
  - name: MY_VAR_FROM_FIELD_REF
    valueFrom:
      fieldRef:
        fieldPath: metadata.labels['my_label']

Environment:

• helm version: 3
• helm chart version and app version: 8.1.0/1.15.0
• Kubernetes version: 1.31