feat(keycloak): Switch to recommended ingress paths

This patch adjusts the keycloak helm chart to use the upstream
recommended paths for exposing keycloak. It also adjusts the current
deployment to utilise a dedicated, further restricted admin interface.

BREAKING CHANGE: This commit will remove the exposure of the admin
interface as well as other exposed URLs.

References:
https://www.keycloak.org/server/reverseproxy#_exposed_path_recommendations