Fix an issue showing attach/detach docs

There's a condition in sub_list_create_api_view.md template that
controls whether or not the attach/detach documentation is shown for
sublist elements that support it.   Looks like it's been this way for a
while.  This updates that condition to work anywhere it's needed

awx/api/generics.py

@@ -360,6 +360,13 @@ class SubListCreateAttachDetachAPIView(SubListCreateAPIView):
     # Base class for a sublist view that allows for creating subobjects and
     # attaching/detaching them from the parent.
 
+    def get_description_context(self):
+        d = super(SubListCreateAttachDetachAPIView, self).get_description_context()
+        d.update({
+            "has_attach": True,
+        })
+        return d
+
     def attach(self, request, *args, **kwargs):
         created = False
         parent = self.get_parent_object()