Make project-clone work in a temporary directory; copy files at end

[amisevsk]

What does this PR do?

In order to avoid issues where the project-clone container is killed during its initial run, leaving repos in a half-configured state, do all operations in a temporary directory and copy repos to their expected locations at the very end.

What issues does this PR fix or reference?

Closes #699

Is it tested? How?

Can be tested using the image quay.io/amisevsk/project-clone:atomic-clone (e.g. in the relevant RELATED_IMAGE env var or by setting PROJECT_CLONE_IMG when installing DWO). To test both git and zip type projects, use the devfile

cat <<EOF | kubectl apply -f - 
kind: DevWorkspace
apiVersion: workspace.devfile.io/v1alpha2
metadata:
  name: theia-next
spec:
  started: true
  template:
    projects:
      - name: web-nodejs-sample
        git:
          remotes:
            origin: "https://github.com/che-samples/web-nodejs-sample.git"
      - name: devworkspace-operator-zip
        zip:
          location: https://github.com/devfile/devworkspace-operator/archive/refs/heads/main.zip
    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
EOF

and check that

1. Projects are setup successfully
2. Project-clone does nothing when the workspace is restarted
3. No temp directories or files are present in $PROJECTS_ROOT
4. (If you can figure out how) kill project clone while it's preparing projects and make sure the subsequent run behaves as above

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

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: amisevsk, JPinkney

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[amisevsk]

/test v8-devworkspace-operator-e2e

[amisevsk]

Validation is failing as os.MkDirTemp was only added in Go 1.16 :(

[amisevsk]

Blocked by #705

[openshift-ci]

New changes are detected. LGTM label has been removed.

[amisevsk]

/test v8-devworkspace-operator-e2e