Add mgmt_type into device metadata YANG model. (sonic-net#21897)

Add mgmt_type into device metadata YANG model.

Author: r12f

src/sonic-yang-models/tests/yang_model_tests/tests/device_metadata.json

@@ -94,6 +94,9 @@
     "DEVICE_METADATA_RESOURCE_TYPE_CONFIG": {
         "desc": "Verifying resource type configuration."
     },
+    "DEVICE_METADATA_MGMT_TYPE_CONFIG": {
+        "desc": "Verifying mgmt type configuration."
+    },
     "DEVICE_METADATA_VALID_CLUSTER": {
         "desc": "Verifying valid cluster configuration."
     },

src/sonic-yang-models/tests/yang_model_tests/tests_config/device_metadata.json

@@ -257,6 +257,15 @@
             }
         }
     },
+    "DEVICE_METADATA_MGMT_TYPE_CONFIG": {
+        "sonic-device_metadata:sonic-device_metadata": {
+            "sonic-device_metadata:DEVICE_METADATA": {
+                "sonic-device_metadata:localhost": {
+                    "mgmt_type": "mgmt_type_x"
+                }
+            }
+        }
+    },
     "DEVICE_METADATA_VALID_CLUSTER": {
         "sonic-device_metadata:sonic-device_metadata": {
             "sonic-device_metadata:DEVICE_METADATA": {

src/sonic-yang-models/yang-models/sonic-device_metadata.yang

@@ -157,6 +157,11 @@ module sonic-device_metadata {
                     type string;
                 }
 
+                leaf mgmt_type {
+                    type string;
+                    description "Indicates the management type of this device.";
+                }
+
                 leaf cluster {
                     type string;
                     description "The switch is a member of this cluster.";