Tacker requires config for storing CSAR vnf packages.
This patch adds it as well as relevant docs.
Only one Tacker Conductor is deployed by default due to
lack of a shared filesystem.

Change-Id: Iad391f35105e79fa9319502256528990915df9b7
Co-authored-by: Radosław Piliszek <radoslaw.piliszek@gmail.com>
Closes-Bug: #1845142