Add validation for monitor URL and update test case and api documentation accordingly

Server/openapi.json

@@ -882,6 +882,16 @@
               }
             }
           },
+          "422": {
+            "description": "Unprocessable Content",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                }
+              }
+            }
+          },
           "500": {
             "description": "Internal Server Error",
             "content": {