refactor inventory Loaders for ansible-inventory

* remove support for loading from executable and static files
* instead use ansible-inventory with fallback to backport
* provide private file dir in task manager for cred injection
* durable management of tmp dirs for user scripts

* new 'scm' source choice for scm-type
* update SCM inventory docs to new reality

awx/api/views.py

@@ -2353,7 +2353,7 @@ class InventorySourceUpdateView(RetrieveAPIView):
 
     def post(self, request, *args, **kwargs):
         obj = self.get_object()
-        if obj.source == 'file' and obj.scm_project_id is not None:
+        if obj.source == 'scm':
             raise PermissionDenied(detail=_(
                 'Update the project `{}` in order to update this inventory source.'.format(
                     obj.scm_project.name)))