Additional info from router (Including headers) does not pass to custom handlers

with configuration like this:
```
...
    "/ping": {
      "handler": {
        "source": "handlers/api.py",
        "get": "get"
      },
      "headers": [
        ["Access-Control-Allow-Origin", "http://localhost:3000"]
      ]
    }
...
```
in `handlers/api.py` its impossible to get `["Access-Control-Allow-Origin", "http://localhost:3000"]` without parsing config again.