distro: add FreeBSD code path for eject

OpenBSD, NetBSD, and Dragonfly all have an eject(1), so they should be
covered in the default code path.

FreeBSD however, does not have eject in base. It's an (unmaintained)
port. In base, we do however, have camcontrol(8) and cdcontrol(1), both
of which have an eject subcommand.

Let's use camcontrol(8) here.

Sponsored by: The FreeBSD Foundation

cloudinit/distros/freebsd.py

@@ -226,3 +226,7 @@ def build_dhclient_cmd(
         return [path, "-l", lease_file, "-p", pid_file] + (
             ["-c", config_file, interface] if config_file else [interface]
         )
+
+    @staticmethod
+    def eject_media(device: str) -> None:
+        subp.subp(["camcontrol", "eject", device])