[SPARK-22475][SQL] show histogram in DESC COLUMN command

## What changes were proposed in this pull request?

Added the histogram representation to the output of the `DESCRIBE EXTENDED table_name column_name` command.

## How was this patch tested?

Modified SQL UT and checked output

Please review http://spark.apache.org/contributing.html before opening a pull request.

Author: Marco Gaido <mgaido@hortonworks.com>

Closes #19774 from mgaido91/SPARK-22475.