VDO support

[JohnStrunk]

Describe the feature you'd like to have. It should be possible to enable VDO in the Gluster pods to get better storage efficiency.

What is the value to the end user? (why is it a priority?) By increasing storage efficiency, we can decrease the cost of the storage infrastructure.

How will we know we have a good solution? (acceptance criteria)

• VDO can optionally be enabled on a set of gluster nodes (probably as a topology template option)
• Physical capacity remaining can be monitored by the operator for expanding/shrinking the cluster

Additional context This depends on VDO support in both the gluster containers and GD2