feat(ws): Notebooks 2.0 // Backend // List Workspaces API and use controller-runtime for backend

[ederign]

curl -i localhost:4000/api/v1/spawner/workspace-test/workspaces

{
  "workspaces": [
    {
      "name": "jupyterlab-workspace-1",
      "kind": "jupyterlab",
      "image": "jupyterlab_scipy_190",
      "config": "tiny_cpu",
      "status": "Running",
      "home_volume": "workspace-home-pvc",
      "data_volume": "/data/my-data",
      "last_activity": "1969-12-31 19:00:00 EST"
    },
    {
      "name": "jupyterlab-workspace-2",
      "kind": "jupyterlab",
      "image": "jupyterlab_scipy_190",
      "config": "tiny_cpu",
      "status": "Running",
      "home_volume": "workspace-home-pvc",
      "data_volume": "/data/my-data",
      "last_activity": "1969-12-31 19:00:00 EST"
    }
  ]
}

Other than that, this PR makes the following changes on top of the referenced PR:

1. Fixes healthcheck handler and it's tests;
2. Create workspace_handler and it's tests
3. Add go mock for testing
4. Create WorkspaceModel BFF type
5. Create Workspace model and GetWorkspaces method
6. mock_workspaces_data.go was generated with ~/go/bin/mockgen -destination=test/mock_client.go -package=mocks sigs.k8s.io/controller-runtime/pkg/client Client

[google-oss-prow]

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