Container images to be used with Rust cross.

Currently included:

• Build dependencies for the dbus crate:
  • dbus-aarch64-gnu (aarch64-unknown-linux-gnu)
  • dbus-armv7-gnu (armv7-unknown-linux-gnueabihf)
  • dbus-armv7-musl (armv7-unknown-linux-musleabihf)

• Use stable base images from ghcr.io/cross-rs/, upgrade to v0.2.4.

• Add dbus-aarch64-gnu.
• Use base images from ghcr.io/cross-rs/ instead of Docker Hub. Pin to the latest "main" until a stable release has been tagged.

• First versions of dbus-arm-gnu and dbus-arm-musl.