logger: add watchdog that boosts its priority when the writer is blocked for >1s

This is to guard against busy-looping tasks, so that we at least have a
log. In case the watchdog is triggered, it also logs CPU load of all
tasks.

src/modules/logger/CMakeLists.txt

@@ -43,6 +43,7 @@ px4_add_module(
 		log_writer.cpp
 		log_writer_file.cpp
 		log_writer_mavlink.cpp
+		watchdog.cpp
 	DEPENDS
 		version
 	)