[che-auth] Setup full che-like auth flow on Kubernetes

[sparkoo]

Is your task related to a problem? Please describe.

We need to prototype a full authentication/authorization flow that we now see as a candidate to new solution for Che.

Describe the solution you'd like

1. setup minikube+dex+oidc (Try to setup minikube + dex + OIDC + RBAC #19196) with multiple users
2. setup oauth2-proxy -> traefik -> demoapp with kube-rbac-proxy as a sidecar
3. setup multiple demoapps in separate namespaces with only concrete user having access to single owned namespace

             |
+- - - - - - | - - - - - - - - - - k8s - - - - - -+
|            |                                    |
             V
|     +--------------+  (oidc)  +-------+         |
      | oauth2-proxy |--------->|  DEX  |
|     +--------------+          +-------+         |
             |                      A
|            V                      |             |
        +---------+                 | (oidc)
|       | traefik |                 |             |
        +---------+         +---------------+
|            |              |    k8s-api    |     |
             |              +---------------+
|            V                      A             |
      +-----------------+           |
|    +-----------------+|           |             |
     | kube-rbac-proxy-||-----------+
|    |       |         ||                         |
     |       V         ||
|    |    demo-app     |+                         |
     +-----------------+
|                                                 |
+- - - - - - - - - - - - - - - - - - - - - - - - -+

Describe alternatives you've considered

Additional context

epic: Authentication and authorization in Eclipse Che #19182

[sparkoo]

POC done in https://github.com/che-incubator/che-auth-playground/tree/master/kubernetes