RestClient Reactive: Support inheritance of sub resources

Allow to use sub resources in client resources:

Usage for first level:
```java
@path("/path")
@RegisterRestClient(baseUri = "http://localhost:8081")
@consumes("text/plain")
@produces("text/plain")
public interface RootResource {

    @path("/sub")
    SubClient sub();
}
```

Second level:
```
@consumes("text/plain")
@produces("text/plain")
interface SubClient {
    @path("/sub")
    SubSubClient sub();
}
```

Third and N levels (this was unsupported and now it's supported):
```
@consumes("text/plain")
@produces("text/plain")
interface SubSubClient {
    @get
    @path("/simple")
    String simpleGet();
}
```

Fix #22055