feat: support "delete" in distributed mode (#28)

proto/greptime/v1/database.proto

@@ -23,6 +23,7 @@ message GreptimeRequest {
     InsertRequest insert = 2;
     QueryRequest query = 3;
     DdlRequest ddl = 4;
+    DeleteRequest delete = 5;
   }
 }
 
@@ -55,3 +56,17 @@ message InsertRequest {
   // The region number of current insert request.
   uint32 region_number = 5;
 }
+
+message DeleteRequest {
+  // The table name to delete from. Catalog name and schema name are in the `RequestHeader`.
+  string table_name = 1;
+
+  // The region number of current delete request.
+  uint32 region_number = 2;
+
+  // The data to delete, indexed by key columns.
+  repeated Column key_columns = 3;
+
+  // The row count of all columns above.
+  uint32 row_count = 4;
+}