Annotate WorkspaceRouting with routing class specific annotations

[metlos]

With the advent of external workspace routing controllers, there has arisen the need to configure them on per-workspace basis. In another words it should be possible to pass down routing class specific configuration to the external controller.

== Proposed Solution

There is a precedent for handling this kind of "polymorphism" in Kubernetes with the Ingress annotations, e.g. https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/annotations/.

I would like to propose configuring the workspace routing controller using annotations on the DevWorkspace object.

Let's say we have a workspace routing controller handling the myrouting routing class.

We would be able to configure it on the DevWorkspace object like this:

kind: DevWorkspace
apiVersion: workspace.devfile.io/v1alpha1
metadata:
  name: cloud-shell
  annotations:
    controller.devfile.io/restricted-access: "true"
    controller.devfile.io/other-cotroller-annotation: "yes"
    myrouting.routingclass.controller.devfile.io/answer: "42"
spec:
  started: true
  routingClass: myrouting
  template:
    ...

This would create a workspace routing object with the 2 following annotations:

kind: WorkspaceRouting
apiVersion: workspace.devfile.io/v1alpha1
metadata:
  name: ...
  annotations:
    controller.devfile.io/restricted-access: "true"
    myrouting.routingclass.controller.devfile.io/answer: "42"
...

The restricted-access is already being passed down by the existing code. myrouting.routingclass.controller.devfile.io/answer is considered a configuration property of the controller and therefore is passed down to the WorkspaceRouting object. controller.devfile.io/other-cotroller-annotation is NOT passed down, because it is unrelated to the workpace routing.

== Alternative Solution

We could also specify the configuration directly in the spec of the Devworkspace, e.g.:

kind: DevWorkspace
apiVersion: workspace.devfile.io/v1alpha1
metadata:
  name: cloud-shell
  annotations:
    controller.devfile.io/restricted-access: "true"
    controller.devfile.io/other-cotroller-annotation: "yes"
spec:
  started: true
  routingClass: myrouting
  routingAnnotations:
    answer: "42"
  template:
    ...

This feels a little bit less idiomatic Kubernetes to me though.

[sleshchenko]

@metlos Could you review if it is fully resolved by #245

[metlos]

Yes, it is