Helm: Add support for ingresses

[zanieb]

Yeah, I think having an ingress shouldn't be on by default (or required), but supporting an opt-in option which requires some user configuration makes sense to me. This is what JupyterHub does as well, and it seems to work well. https://zero-to-jupyterhub.readthedocs.io/en/latest/administrator/advanced.html#ingress, https://github.com/jupyterhub/zero-to-jupyterhub-k8s/blob/master/jupyterhub/templates/ingress.yaml.

Originally posted by @jcrist in #123 (comment)

Also see an example at https://devspace.sh/component-chart/docs/configuration/ingress

May be blocked by UI changes -- will update this note once I have more infomration.