Add option to run command after inactivity delay (closes #747)

Signed-off-by: AnErrupTion <anerruption@disroot.org>

src/config/Lang.zig

@@ -24,6 +24,7 @@ err_envlist: []const u8 = "failed to get envlist",
 err_get_active_tty: []const u8 = "failed to get active tty",
 err_hibernate: []const u8 = "failed to execute hibernate command",
 err_hostname: []const u8 = "failed to get hostname",
+err_inactivity: []const u8 = "failed to execute inactivity command",
 err_lock_state: []const u8 = "failed to get lock state",
 err_log: []const u8 = "failed to open log file",
 err_mlock: []const u8 = "failed to lock password memory",