Add filename as valuesKey for valuesFrom of type SylvaUnitsFile

closes #76 (closed)

Tested locally.

Filename is being added as valuesKey in the helmRelease valuesFrom

kubectl get hr sylva-units -n sylva-system -o yaml | yq '.spec.valuesFrom'
- kind: Secret
  name: sylva-units-file-01cdd13a
  valuesKey: management.values.yaml

kubectl get secret sylva-units-file-01cdd13a -n sylva-system -o yaml
apiVersion: v1
data:
  management.values.yaml: xxxxxxxxxxxxx