[ssip]: Update YANG doc. (#11363)

- Why I did it
To implement Syslog Source IP feature

- How I did it
Added the relevant yang doc

- How to verify it
N/A

Signed-off-by: Nazarii Hnydyn <nazariig@nvidia.com>

src/sonic-yang-models/doc/Configuration.md

@@ -1123,6 +1123,24 @@ attributes in those objects.
         "10.0.0.5": {},
         "10.0.0.6": {},
         "10.11.150.5": {}
+    },
+
+    "SYSLOG_SERVER" : {
+        "2.2.2.2": {
+            "source": "1.1.1.1",
+            "port": "514",
+            "vrf": "default"
+        },
+        "4.4.4.4": {
+            "source": "3.3.3.3",
+            "port": "514",
+            "vrf": "mgmt"
+        },
+        "2222::2222": {
+            "source": "1111::1111",
+            "port": "514",
+            "vrf": "Vrf-Data"
+        }
     }
 }
 ```