* feat: add generic lnurl error response handler
this is used multiple times in extensions to safeguard `views_lnurl.py`
endpoint to not return a wrong lnurl error response.
you use it by just setting following on your lnurl router/view
```
withdraw_ext_lnurl = APIRouter(prefix="/api/v1/lnurl")
withdraw_ext_lnurl.route_class = LNURLErrorResponseHandler
```