[SPARK-14470] Allow for overriding both httpclient and httpcore versions

## What changes were proposed in this pull request?

This splits commons.httpclient.version from commons.httpcore.version, since these two versions do not necessarily have to be the same.  This change may follow up with an up-to-date version of the httpclient/httpcore libraries.

The latest 4.3.x httpclient version as of writing is 4.3.6 and the latest 4.3.x httpcore version as of writing is 4.3.3.  This change would be a prerequisite for potentially moving to this new bugfix version.

## How was this patch tested?
no version change was made for httpclient/httpcore versions
mvn package

Author: Aaron Tokhy <tokaaron@amazon.com>

Closes #12245 from atokhy/pull-request.