Fixes judgehost down notification

[tuupke]

The route requires the judgehostid as route parameter, not the hostname.

Currently clicking the notification results in the screen shown below. Arguably this should be a 4xx error, but then it should be fixed within all route specifications by appending <\d+> to the parameter name. e.g.:

#[Route(path: '/{judgehostid}', methods: ['GET'], name: 'jury_judgehost')]
to 
#[Route(path: '/{judgehostid<\d+>}', methods: ['GET'], name: 'jury_judgehost')]

[tuupke]

@nickygerritsen is changing things in #3024 to use external ids (strings) everywhere but here. So will add that change here too.