Create trait for NUMA subtree affinity

Introduce trait HW_NUMA_ROOT. This is to be used with the 'resourceless
RP' and 'same_subtree' placement features [1] when requesting NUMA
affinity (e.g. multiple devices affined to the same NUMA node)
especially when not requesting resources from the subtree root provider
itself.

[1] https://review.opendev.org/#/c/662191/
Change-Id: If5478e797b7bec2d8ebe78dd959dcf179a2834f4
Story: #2005575
Task: #30908

os_traits/hw/numa/__init__.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+# Characteristics of NUMA nodes/cells/sockets/etc.
+TRAITS = [
+    # A provider representing the subtree root of a NUMA node should be
+    # decorated with this trait so that requests can represent NUMA affinity
+    # even when no resources are requested from the NUMA node provider itself.
+    # See https://review.opendev.org/#/c/662191/
+    'ROOT',
+]