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()

awx/api/templates/api/sub_list_create_api_view.md

@@ -12,7 +12,7 @@ fields to create a new {{ model_verbose_name }} associated with this
 
 {% block post_create %}{% endblock %}
 
-{% if view.attach %}
+{% if has_attach|default:False %}
 {% if parent_key %}
 # Remove {{ parent_model_verbose_name|title }} {{ model_verbose_name_plural|title }}:
 

awx/api/views.py

@@ -2453,7 +2453,6 @@ class JobTemplateLabelList(SubListCreateAttachDetachAPIView, DeleteLastUnattachL
     serializer_class = LabelSerializer
     parent_model = JobTemplate
     relationship = 'labels'
-    parent_key = 'job_template'
 
 class JobTemplateCallback(GenericAPIView):