Insufficient implementation in v4.0.1

1. Dynamic service registration is not supported in `dubbo.ts`, services registration is executed only once by `init()`，which means you have to collect services before dubbo `init` carefully.
2. May I custom `attachments` in individual method invoking? such as: traceId, ua, even userId which changes when users make requests.

Ideas above may be incorrect, just for communication.
Thank you for the excellent open source contribution!