Support providing additional labels to deployments' pods

[jabbera]

I need to add an additional label to the api gateway pod to apply an azure ad pod identity. JupyterHub allows this customization with the extraLabels option as seen here: https://github.com/jupyterhub/zero-to-jupyterhub-k8s/blob/204ec021454dbb4d7c23c524ac313dfc3d05ee2a/jupyterhub/values.yaml#L350

Edit: Ability to customize environment variables would be great also. In the meantime I can use extraConfig for this.

I'd love the same customizability here.