feat: add ddl task service (#53)

* feat: add ddl task service

* chore: apply suggestions from CR

* chore: add path to build.rs

proto/greptime/v1/meta/ddl.proto

@@ -0,0 +1,64 @@
+// 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";
+
+package greptime.v1.meta;
+
+option go_package = "github.com/GreptimeTeam/greptime-proto/go/greptime/v1/meta";
+
+import "greptime/v1/meta/common.proto";
+
+service DdlTask {
+    // Submits a DDL task to meta.
+    rpc SubmitDdlTask(SubmitDdlTaskRequest) returns (SubmitDdlTaskResponse);
+}
+
+enum DdlTaskType {
+    Create = 0;
+}
+
+message Task {
+    DdlTaskType type = 1;
+    
+    oneof payload { bytes pd = 2; }
+}
+
+message SubmitDdlTaskRequest {
+    RequestHeader header = 1;
+
+    // The following information plays a bigger role in making messages traceable
+    // and facilitating debugging.
+    string subject = 2;
+    string from = 3;
+    string to = 4;
+    // The unix timestamp in milliseconds.
+    int64 timestamp_millis = 5;
+    
+    Task task = 6;
+}
+
+enum Status {
+    Done = 0;
+    Failed = 1;
+    Cancelled = 2;
+}
+
+message SubmitDdlTaskResponse {
+    ResponseHeader header = 1;
+    // Key is the identifier for the ddl task.
+    bytes key = 2;
+
+    Status status = 3;
+}