polyline width as parameter on geofence

Distance around polyline geofence when device considered "inside geofence" can be configured with geofence.polylineDistance configuration
parameter (25 meters by default).

It would be nice to have this as a parameter on the polyline itself, to avoid having to change files on the server

For feature requests you should use GitHub.

It was implemented some time ago https://github.com/traccar/traccar/pull/3838 , and available in current release. You can use Geofence attributes to set it.