schemas: legacy: extract NMSensor

Node Manager Sensor is only configured once and unclear what it is used
for.

Create a schema anyways for completeness sake.

Tested: Schema Validator Pass

Change-Id: Ibb46dcbca8904469a2fb36c8afd562164fcb731b
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/global.json b/schemas/global.json
index 8fdbc81..28a174c 100644
--- a/schemas/global.json
+++ b/schemas/global.json
@@ -121,6 +121,9 @@
                             "$ref": "legacy.json#/$defs/PSUSensor"
                         },
                         {
+                            "$ref": "legacy.json#/$defs/NMSensor"
+                        },
+                        {
                             "$ref": "virtual_sensor.json#/$defs/VirtualSensor"
                         },
                         {