feat: adds MergeScan plan node (#172)

* feat: adds dist_plan to substrait_extension

* feat: adds table_names to CreateViewExpr

* chore: style

Co-authored-by: Jeremyhi <jiachun_feng@proton.me>

* fix: update genearted code

---------

Co-authored-by: Jeremyhi <jiachun_feng@proton.me>

proto/substrait_extension/dist_plan.proto

@@ -0,0 +1,26 @@
+// Copyright 2023 Greptime Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+option go_package = "github.com/GreptimeTeam/greptime-proto/go/substrait_extension";
+
+package substrait_extension;
+
+message MergeScan {
+  // the input logical plan
+  bytes input = 1;
+  // whether this plan is a placeholder
+  bool is_placeholder = 2;
+}