feat: truncate table (#70)

proto/greptime/v1/ddl.proto

@@ -34,6 +34,7 @@ message DdlRequest {
     DropTableExpr drop_table = 4;
     FlushTableExpr flush_table = 5;
     CompactTableExpr compact_table = 6;
+    TruncateTableExpr truncate_table = 7;
   }
 }
 
@@ -93,6 +94,13 @@ message CreateDatabaseExpr {
   bool create_if_not_exists = 2;
 }
 
+message TruncateTableExpr {
+  string catalog_name = 1;
+  string schema_name = 2;
+  string table_name = 3;
+  TableId table_id = 4;
+}
+
 message AddColumns { repeated AddColumn add_columns = 1; }
 
 message DropColumns { repeated DropColumn drop_columns = 1; }