[Photon] missing support for multiple layers

[fbuchlak]

#1245 introduced layer parameter for photon.

Photon supports filtering by multiple layers.

https://photon.komoot.io/reverse?lat=49.001831&lon=21.239311&layer=city&limit=5
https://photon.komoot.io/reverse?lat=49.001831&lon=21.239311&layer=city&layer=district&limit=5

However it's not possible to filter with multiple layers with Geocoder\Provider\Photon\Photon.