Hello, I would like to propose adding support for SystemD socket activation.

This brings the following advantages:

• Enables delayed program startup, allowing Quantum to run only when a connection is requested.
• No 502 errors during program restarts, as Systemd keeps the socket open, resulting in just a slightly longer load time for clients while the service restarts.
• Free Unix socket support, meaning connections can be managed with classic Unix file permissions, eliminating the "which port did I use" guessing game and offering a minor performance boosts when using a reverse proxy on the same machine.
• Improved performance with Podman, as socket activation bypasses the containerized network, making it as efficient as using the host network.
• With Podman, containers can run without a network since socket activation doesn't depend on it.
• It makes long-bearded Linux admins happy.

I imagine this addition would introduce minimal code complexity since Go's net package handles much of the intricacies of various socket types. Additionally, libraries like CoreOS's go-systemd could simplify the process even more.

If there's interest in this feature, I'd be happy to volunteer to write a PR.