Document OIDC configuration options in values for kcp chart

[embik]

It looks like we have a ton of OIDC configuration values (see

helm-charts/charts/kcp/templates/front-proxy-deployment.yaml

Line 86 in c6fd2c2

{{- if .Values.oidc.enabled }}

) that are not mentioned in any way in the values.yaml file.

It's not a good user experience if users need to go digging in templates to figure out which options are available. We should document all of them in charts/kcp/values.yaml by default.