dashboard: add opt-in for full external login (e.x. oauth-proxy)

[gberche-orange]

Problem

As a dashboard operator
in order to deploy the dashboard on K8S clusters without an IDP configured but with an available oauth-proxy facing the dashboard
I need to configure the dashboard to skip the login page

Solution

a helm option such as "skipLogin: true" which enables be automatically logged in with the default admin user.

This option would typically be used in conjonction with the https://oauth2-proxy.github.io/oauth2-proxy/ as to still secure access to the dashboard

Workaround

Configure a dummy user (e.g. login=admin password=admin)

Additional context

[makkes]

@foot fyi