Feature Request: Add support for StalledDiskPrimary recoveries by vtorc

[joekelley]

Feature Description

At HubSpot we have had a handful of incidents where a primary becomes impaired due to disk issues. When this happens, we observe that vtorc assigns an UnreachablePrimary analysis which leads to a no-op recovery because the FullStatus
call it makes to the tablet times out. We monitor for these cases outside of Vitess and resolve them by running ERS, but it would be ideal if vtorc could detect and address these cases itself.

Use Case(s)

This recovery would be useful when:

• a hardware/infrastructure fault leads to the disk becoming unavailable.
• a primary enters a sustained period of severe i/o latency where a failover is preferable to waiting for the underlying issue to be resolved.