🔖 Release 0.3.0.

• ✨ Implement Monitoring interface. This means, you can now monitor the bus using busctl monitor.
• ✨ Add --ready-fd that allows busd to notify its parent (usually a service manager) that it is
  ready to accept new incoming connections. This information can then be used by the service manager
  to ensure that dependant services are only started after the broker is ready to accept incoming
  connections. #27
• ⚡️ Use new zbus::socket::Channel for self-dial connection. This should improve the performance
  of our own D-Bus API since it avoids deserialization and re-allocation on the receiver side.
• ⚡️ Enable LTO for release builds.
• 🚨 Explicit lifetimes for constant string literals.
• 👽️ Port to zbus 4 API. This also implies bumping required versions of shared depdendencies, like
  event-listener and tokio.
• ⬆️ Update dependencies:
  • zbus to 4.2.0.
  • serde to 1.0.199.
  • anyhow to 1.0.82.
  • tokio to 1.37.0.
  • clap to 4.5.4.
  • nix to 0.28.0.
  • console-subscriber to 0.2.0.
  • xdg-home to 1.1.0.
  • tracing-subscriber to 0.3.18.
  • tracing to 0.1.40.
  • futures-util to 0.3.30.
  • enumflags2 to 0.7.9.
• ⬆️ Bump MSRV to 1.74.
• ➕ Add a direct dep on event-listener. We indirectly depended on it already.
• 📝 CONTRIBUTING: Drop inexistent gitmoji blog post link.
• ✏️ CONTRIBUTING: Fix a few typos and sync with zbus.
• 🩹 Fix some unused imports for non-unix target.
• 🔥 Drop bogus import of anyhow::Ok.
• 🍱 Add our logo to README.
• ✨ Many internal fixes and improvements.