Add the Profile Sync Daemon Package & NixOS Module

Wasn't exactly sure what categories/subdirectories to put these under. It's a daemon that syncs your web browser profiles to tmpfs to increase speed/responsiveness & decrease ssd writes.
This was just the upstream default. Not sure about I/O levels but the daemon is just a wrapper around rsync.

I think an option is a good idea. Some might just want the speediness, some might not want the disk wear.