Epic Goal

• Add support to MTC for handling migration of PVs which are using 'volumeMode=Block'.

Why is this important?

• As of ~k8s 1.18 volumeMode=Block was added, we believe that future OCP 4.x->4.x migrations will expect support for Block PV migration.

Scenarios

1. MTC is able to migrate a database workload using a raw block device PV between clusters in same cloud region, consider example with EBS.
2. [Explore, unsure if technically possible]: MTC is able to migrate a database workload using a raw block device PV between clusters in different cloud regions, consider example with EBS.
3. [Explore, unsure if technically possible]:  MTC is able to migrate a database workload using a raw block device PV between storage providers?  Consider a on-prem cluster to cloud.  

Acceptance Criteria

• Documentation states capabilities of what MTC can handle with Block PVs, notes if storage class conversion is possible, migration between cloud regions, onprem to cloud, etc.   

Open questions::

1. Is it possible to develop a fallback approach for Block PVs which can always be used and is not dependent on snapshot support.  This is assumed to be poor performance and not recommended as first choice, but could be a last resort for flexibility.
2. Is it possible to do something like a 'dd' to copy bytes and transfer to different regions?  
3. Is it possible to change storageclass providers via raw block device copy of data?

Done Checklist

• CI - CI is running, tests are automated and merged.
• Release Enablement <link to Feature Enablement Presentation>
• DEV - Upstream code and tests merged: <link to meaningful PR or GitHub Issue>
• DEV - Upstream documentation merged: <link to meaningful PR or GitHub Issue>
• DEV - Downstream build attached to advisory: <link to errata>
• QE - Test plans in Polarion: <link or reference to Polarion>
• QE - Automated tests merged: <link or reference to automated tests>
• DOC - Downstream documentation merged: <link to meaningful PR>