feat: download client

[Fuochi]

• add downloadclientconfig (radarr,readarr,lidarr)
• add remotepathmapping (radarr,readarr,lidarr)
• add downloadclient (radarr,readarr,lidarr,prowlarr)

Since remotepathmapping is the same in each arr, we can put the struct definition in the starr package. @davidnewhall what do you think? should we keep each file separate, or should we group the struct definition in one place?

the other 2 resources change a bit between different arr