Broken v6 Import Process

Currently, the import process for a v6 app is broken. One of the key reasons is the removal of mapping types in v6 apps, where we support passing types in the importer UI.

The types dropdown (and selection) should be disabled for v6 apps. Using the following endpoint https://rest.appbase.io/#6c6eff02-2afd-b1fb-b62d-d8b4a146c0fe, we can check the version of the app.


Instead, we should default to `_doc` as the type name or when an app's type exists, pick that instead.