Enable mounting of a shared PVC into multiple deployments

[zsinnema]

For some applications it would be really nice if we could mount a "shared" PVC into multiple deployments.
There are apps where the frontend and the backend are different deployments. E.g. the frontend is a NXING serving a static react app and the backend is a Flask/Django server.

For user content (uploaded content) the application would benefit from sharing a PVC between the frontend and the backend.
The backend will store the uploaded content (e.g. file) and the frontend will serve the file back to the user.

We can do this by adding a volume object to the harness.deployment of the microservices. The issue is that when I have 2 or more services the PVC is multiple times created.

solution proposal:
add the attribure auto to the harness.deployment.volume object.
when true: create the PVC
when false: don't create the PVC