Add per-user storage-class option

[AObuchow]

The 'per-user' storage type is an alternate storage-type name for the 'common' storage class.
In other words, it is an alias for the 'common' storage-type and behaves in the same manner.

Note that in the PR's current state, the 'per-user' storage-type replaces the 'common' storage-type, and the 'common' storage-type is treated as an alias of the 'per-user' storage-type. It may be better to reverse things, i.e. document that the 'per-user' storage-type is an alias of the 'common' storage-type

What issues does this PR fix or reference?

Part of eclipse-che/che#21405

Is it tested? How?

There are two parts of this PR to test.
Ensuring that the 'per-user' storage type works the same as the 'common' storage type:

1. Start up DWO
2. Create and apply a devfile that uses the 'per-user' storage type, e.g.

kind: DevWorkspace
apiVersion: workspace.devfile.io/v1alpha2
metadata:
  name: theia-next
spec:
  started: true
  template:
    attributes:
        controller.devfile.io/storage-type: per-user
    projects:
      - name: web-nodejs-sample
        git:
          remotes:
            origin: "https://github.com/che-samples/web-nodejs-sample.git"
    components:
      - name: theia
        plugin:
          uri: https://che-plugin-registry-main.surge.sh/v3/plugins/eclipse/che-theia/next/devfile.yaml
          components:
            - name: theia-ide
              container:
                env:
                  - name: THEIA_HOST
                    value: 0.0.0.0
    commands:
      - id: say-hello
        exec:
          component: theia-ide
          commandLine: echo "Hello from $(pwd)"
          workingDir: ${PROJECTS_ROOT}/project/app

3. Ensure that the workspace starts up and that the claim-devworkspace PVC is created.
4. Delete the workspace and ensure that the claim-devworkspace PVC is deleted.

Ensuring that you can switch between the 'per-user' and 'common' storage-type:

1. Start up DWO
2. Create and apply 2 devfiles, one with the 'per-user' storage-type and the other with the 'common' storage-type
3. After the workspaces are started up, do a kubectl edit or oc edit and change their storage-type from per-user -> common and common -> per-user respectively
4. Ensure the edit is allowed by the webhook

PR Checklist

• E2E tests pass (when PR is ready, comment /test v8-devworkspace-operator-e2e, v8-che-happy-path to trigger)
  • v8-devworkspace-operator-e2e: DevWorkspace e2e test
  • v8-che-happy-path: Happy path for verification integration with Che

[ibuziuk]

LGTM, but could you please add some tests

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: amisevsk, AObuchow, ibuziuk

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[openshift-ci]

New changes are detected. LGTM label has been removed.

[AObuchow]

LGTM, but could you please add some tests

I added a test to ensure that the CommonStorageProvisioner is used given a devfile that uses the per-user storage class. I haven't been able to think of a better way to test this feature so far.