Optimize History GC for Compliance Oriented Use Cases

Many compliance based use cases require prompt removal of select data from disk, including all history. In practice this can require both row deletes and erasing or masking of data within a column.

The initial version of tablet history GC being worked on in KUDU-236 will not be able to support the SLA of such compliance oriented use cases. This request is to address improving the ability of tablet history GC to accommodate these types of deletes within a very short period of time (1-3 days). Ideally this could be configured on a transaction level, since not all record updates on a table are for compliance reasons.