I added missing `service`tags to some routes. One route had service=national and one had service=international. I've corrected these values to high_speed as it is correct for those trains. For some only the routes and not the route_master relations had the service tag, in those cases I've copied the tags to route_master tags.

My primary motivation was that OsmAPP shows trains that show at a specific station, these trains get categorized in the categories provided by the service tag. Previously there were a few trains at Frankfurt central station which OsmAPP couldn't recognize the type of. This edit changed it so that all trains get categorized.
Here is the station in OsmAPP: https://osmapp.org/node/205364328