Add option to configure blockNewUsers

[mrsimonemms]

When creating a Gitpod instance, it would make sense to prevent users from being able to sign up to that instance. As many users will be enterprises with a specific domain name, this should be considered an easy win

Config to allow gitpod.io users to login

blockNewUsers:
  enabled: true
  passlist: 
    - gitpod.io

[csweichel]

can we please start adding those things to experimental config? It looks like we're inflating the installer config surface without need.

[mrsimonemms]

This is already in the Installer config block and has been ever since the first iteration you did back in August. This ticket is to add this config to KOTS

This shouldn't go into the experimental block as this is something that self-hosted admins use and require