Support proto3 optional with grpc_tools_node_protoc_plugin

### Problem description
I'm using rules_proto_grpc to generate node targets which are consumed by typescript (ts_project from rules_nodejs). rules_proto_grpc uses grpc_tools_node_protoc_plugin from the grpc-tools package to build a js_grpc_node_library. Building a js_grpc_node_library from a file (hello.proto) with an optional field results in the following error message:

```
hello.proto: is a proto3 file that contains optional fields, but code generator protoc-gen-grpc_node_plugin hasn't been updated to support optional fields in proto3. Please ask the owner of this code generator to support proto3 optional.--grpc_node_plugin_out:
```

### Reproduction steps
Use [js_grpc_node_library](https://rules-proto-grpc.com/en/latest/lang/js.html#js-grpc-node-library) to compile a proto with an optional field. For example:

`hello.proto`:
```
syntax = "proto3";

package hello.proto;

message Hello {
optional string greeting = 1;
}
```

`BUILD`:
```
proto_library(
name = "hello_proto",
srcs = glob(["*.proto"]),
)

js_grpc_node_library(
name = "hello_js_grpc",
protos = [":hello_proto"],
)
```

### Environment
- OS: Linux Ubuntu 20.04 amd64
- Node version: 16.12
- Node installation method: bazel rules_nodejs
- grpc-tools@1.11.2 (https://github.com/rules-proto-grpc/rules_proto_grpc/blob/master/js/requirements/package.json#L5)