Support VTPKs as basemap and operational layers

[kerryrobinson]

Description

We should enhance DSA to support VTPKs for basemaps and as operational layers.

In the doc, we can reference these topics/links regarding how to download maps/data as vtpks for use:

• Take a map offline | ArcGIS Pro documentation
• Vector Basemaps (for Export) - Overview

Definition of Done

• User can add vtpks to the BasemapData folder, and app will include it in the list of basemaps to choose from
• User can add vtpks to the OperationalData folder, and app will include it in the list of operational data to load
• Guide doc (doc/readme.md) is updated.