fix: allow arbitrary env keys eg valueFrom

[lizthegrey]

No description provided.

[lizthegrey]

Testing this against my own vendored copy, will report back...

[kolesnikovae]

Thank you for the contribution @lizthegrey!

Yeah, I think we should keep the current behavior of env for backward compatibility. We can introduce an additional variable, although it will be difficult to combine them.

Alternatively, since the main scenario for this is using secrets, we could use the envFrom directive:

{{- if .Values.envFromSecret }}
envFrom:
- secretRef:
    name: {{ .Values.envFromSecret }}
{{- end }}