Inventory.Item: add namespace path constant

Add path constant that allow code to avoid hard-coding strings,
matching the requirements outlined in the description section of the
YAML.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I9d79f0301cd7132c3c879330a71147c3fc8f620e
diff --git a/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml b/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml
index 209a6d0..9832867 100644
--- a/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml
+++ b/yaml/xyz/openbmc_project/Inventory/Item.interface.yaml
@@ -87,3 +87,6 @@
       reverse_name: monitoring
       required_endpoint_interfaces:
           - xyz.openbmc_project.Chassis.Intrusion
+
+paths:
+    - namespace: /xyz/openbmc_project/inventory