fix #21634: Download Along: Allow user to configure if there's a confirmation dialog for small number of download requests.

[amandasaurus]

DownloadAlong will ask the user to confirm if it wants to make more than 1 download request. With this patch, the user can set a preference (downloadAlongWay.numDownloadRequestConfirmation or downloadAlongTrack.numDownloadRequestConfirmation), and JOSM will not ask for confirmation if it would make less than or equal to this many requests. If this preference isn't set, it's assumed to be 1. i.e. JOSM will require confirmation when it would make more than 1 request, which is the current behaviour.

I made this patch because I don't want the extra step for making (e.g.) 5 requests.

Please feel free to review it and give feedback. I'm not very experienced with java.

see also https://josm.openstreetmap.de/ticket/21634