New JSON Top-Level Object: Add compaction reason as a parent category in the same manner flush reason is.

[udi-speedb]

The "Flushes" JSON top level object has a sub-object per cf, and, for every cf, a sub-object per every flush reason.
The equivalent for compactions is the compaction reason.
So, this feature is a request to add the compaction reason to the "Compactions" top-level object as it is done for Flushes.