Add initial systemd lifecycle notification support

[bastelfreak]

Code adapted with permission of the original author (this author) from
nrepl socket.clj.

cf. https://www.freedesktop.org/software/systemd/man/sd_notify.html

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This is a refactored version of #20

[bastelfreak]

This is now working properly. I did a build with:

DEP_REBUILD=clj-parent,trapperkeeper DEP_REBUILD_ORG=bastelfreak DEP_REBUILD_BRANCH=sd_notify_2 EZBAKE_VERSION=2.8.0-SNAPSHOT EZBAKE_REPO='https://github.com/bastelfreak/ezbake' EZBAKE_BRANCH='notify' DEB_PLATFORMS='ubuntu-24.04' RPM_PLATFORMS='' bundle exec rake vox:build

Trapperkeeper will then check if the environment variable NOTIFY_SOCKET is set. systemd sets it by default when Type=notify or Type=notify-reload is set. Trapperkeeper will inform systemd when the service is started or reloaded. And the service can be reloaded via systemd. trapperkeeper will issue inform systemd about the successful start/reload after [p.s.m.master-service] Puppet Server has successfully started and is now ready to handle requests / after the first jruby instance is up and running.

To actuallly use this feature, we will have to update ezbake to switch to Type=notify-reload in the service section.

[rbrw]

While I haven't reviewed the changes carefully, I did notice that the new version will now suppress a send error (via .send SocketException) and log it as a connection error. The original code was intentionally limiting the scope of that catch to the .connect because connect exceptions are expected, while .send exceptions are not.