Add support for site collection app catalogs... supported added to core APIs

Ref: https://docs.microsoft.com/en-us/sharepoint/dev/general-development/site-collection-app-catalog#configure-and-manage-site-collection-app-catalogs

Potentially affected commands

• site app add
• site app deploy
• site app get
• site app install
• site app list
• site app remove
• site app retract
• site app uninstall
• site app upgrade