Add support for nodeSelector in nginx-gateway-fabric helm chart

[leandrocostam]

Is your enhancement request related to a problem? Please describe.
Yes. I am not able to define nodeSelector for the nginx-gateway-fabric deployment.

What would you like to be added:
Support to define nodeSelector for the nginx-gateway-fabric deployment.

Why this is needed:
nodeSelector is the simplest recommended form of node selection constraint in Kubernetes.