Implement Volume component

[sleshchenko]

It's needed to implement Volume component that will define PVC or emptyDir with size configuration.

components:
  - name: maven
    container:
      image: registry.redhat.io/codeready-workspaces/stacks-java-rhel8:2.1
      mountSources: true
      volumeMounts:
        - name: my-storage
          path: /home/jboss/.settings
  - name: my-storage
    volume:
      size: 500Mi

If component references non-declared volume - devworkspace should fail to start or failed to be created?
Probably failed to start since such validation needs external resources to be fetched like in plugins case. See below.

? mountSource: true should be converted to volume with name projects?

Volume can be reused/configured from plugin. Like here https://github.com/devfile/api/blob/master/samples/devfiles/spring-boot-http-booster-devfile.yaml.

...
components:
  - name: java-support
    plugin:
      id: redhat/java8/latest
      components:
        - name: vscode-java            
          container:
            memoryLimit: 2Gi
        - name: m2 # it already has volume define we just configure it
          volume:
            size: 2G
...
  - name: maven-tooling
    container:
      image: registry.redhat.io/codeready-workspaces/stacks-java-rhel8:2.1
      mountSources: true
      memoryLimit: 768Mi
      volumeMounts:
        - name: m2 # using volume from plugin definition
          path: /home/jboss/.m2

Which PVC strategy we should support in devworkspace? Probably common only - one PVC for one namespace. Should we implement the same isolation mechanism as for Che?

- PVC structure:
/workspaceId1
  /volumeName1
  /volumeName2
/workspaceId2
  /volumeName1
  /volumeName2

? Since plugins need volumes in initContainers, we can face issues with initSubpaths from initContainer

devworkspace-operator/pkg/controller/workspace/provision/deployment.go

Line 312 in 1b1bc9e

func precreateSubpathsInitContainer(workspaceId string) corev1.Container {

and probably we need to run a separate job to do it