api: support gRPC and provide SDKs

Compare to exited RESTful API, gRPC is more efficient for communications among servers.

## Design

For each API, move current implementation to a shared handler, and call this shared handler from RESTful API handler as well as gRPC API handler.

```
┌───────────┐ ┌───────────┐
│RESTful API│ │ gRPC API │
└─────────┬─┘ └─┬─────────┘
│ │
┌─▼─────▼─┐
│ Handler │
└─────────┘
```

## Tasks

- [ ] gRPC APIs
- [ ] Gorse Go SDK
- [ ] Gorse Java SDK
- [ ] Gorse Rust SDK
- [ ] Gorse Python SDK
- [ ] Gorse Node.js SDK