[New Module Request] handlr

### Program/Service Name handlr ### Upstream Repository https://github.com/chmln/handlr ### Configuration Documentation It seems that handlr writes and reads the same file as xdg-utils. So perhaps the way home-manager could use it is at build time, for implementing the wildcards, and it would be mutually exclusive with `xdg.mimeApps.defaultApplications`. ### Reason for Addition What frustrates me the most about xdg-utils is the lack of wildcards. Like, why can't I just do `video/*` or `audio/*`? Who cares what the format is? Or, if I do want to override one specific format, I'd want to to something like `video/*:vlc,video/mp4:other-player`. handlr seems to cater to the needs of actual users in this manner.