feat: impl insert for DistTable (#406)

* feat: impl insert for dist_table in frontend

* add the logic of decode region id in datanode.

src/datanode/src/instance/grpc.rs

@@ -1,3 +1,6 @@
+use std::ops::Deref;
+
+use api::v1::codec::RegionId;
 use api::v1::{
     admin_expr, codec::InsertBatch, insert_expr, object_expr, select_expr, AdminExpr, AdminResult,
     ObjectExpr, ObjectResult, SelectExpr,
@@ -200,6 +203,18 @@ impl GrpcQueryHandler for Instance {
                     .context(servers::error::InvalidQuerySnafu {
                         reason: "missing `expr` in `InsertExpr`",
                     })?;
+
+                // TODO(fys): _region_id is for later use.
+                let _region_id: Option<RegionId> = insert_expr
+                    .options
+                    .get("region_id")
+                    .map(|id| {
+                        id.deref()
+                            .try_into()
+                            .context(servers::error::DecodeRegionIdSnafu)
+                    })
+                    .transpose()?;
+
                 match expr {
                     insert_expr::Expr::Values(values) => {
                         self.handle_insert(table_name, values).await