[ONNX] Enable ScatterND operator in ONNX importer (#1987)

* Enable ONNX scatter_nd

* Tests update

ngraph/test/models/onnx/scatter_nd_const_i32_indices.prototxt

@@ -0,0 +1,64 @@
+ir_version: 3
+producer_name: "nGraph ONNX Importer"
+graph {
+  node {
+    input: "x"
+    input: "i"
+    input: "u"
+    output: "y"
+    op_type: "ScatterND"
+  }
+  name: "test_scatterND"
+  input {
+    name: "x"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 8
+          }
+        }
+      }
+    }
+  }
+  initializer {
+    dims: 4
+    dims: 1
+    data_type: 6
+    int32_data: 4
+    int32_data: 3
+    int32_data: 1
+    int32_data: 7
+    name: "i"
+  }
+  input {
+    name: "u"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 4
+          }
+        }
+      }
+    }
+  }
+  output {
+    name: "y"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 8
+          }
+        }
+      }
+    }
+  }
+}
+opset_import {
+  version: 7
+}

ngraph/test/models/onnx/scatter_nd_param_i64_indices.prototxt

@@ -22,7 +22,7 @@ graph {
       }
     }
   }
-   input {
+  input {
     name: "i"
     type {
       tensor_type {
@@ -38,7 +38,7 @@ graph {
       }
     }
   }
-    input {
+  input {
     name: "u"
     type {
       tensor_type {