Support Handshake Names on Flux Domain Manager

[flikites]

Please make it easy to deploy and configure Flux Domain Manager so that:

a) FDM can be hosted and accessed from a server with a handshake domain.

b) so applications can add custom handshake domains to their apps

This is a good place to start. https://blog.htools.work/posts/hns-pdns-nginx/ https://blog.htools.work/posts/hnsd-raspberry-pi-zero/