etc: add hnsd systemd service

[tuxcanfly]

WIP: looking for feedback to improve defaults, conflicts with other resolvers, tests on various linux distros etc.

[tuxcanfly]

So I don't think the config file is actually being parsed. Instead what I've done is pass the config options as command line params through the use of EnvironmentFile directive in systemd service.

[tynes]

Since hnsd.conf is no longer being parsed as a config file, should it be renamed to something like hnsd.env and have each of the possible environment variables in it but commented out? We would also need to add the environment variable parsing to hnsd for this to work.

[tynes]

Were you planning on removing $HNSD_CONFIG?

[tuxcanfly]

No, its injected from /etc/hnsd.conf. It's a bit of hack to resemble a configuration file, but all it does is set the env var that gets passed to the executable.

This is only necessary since we don't have config parsing as of yet.

[faddat]

I'd just recommend that flags be used and a sane default be put in the service file.

eg:

hnsd -r 127.0.0.1:53