When idf.py gdb starts, it expects openocd was started in the background
and creates a thread to watch for openocd errors. when gdb target exits,
the debug_ext.py aims to cleanup all threads and processes, but fails
with traceback if openocd-watch thread not available, which could happen
if openocd started separately.
Support for execution of asynchronous target, such as openocd, which
by default runs in the background, but if it's the only target idf.py
outputs the openocd in the console waiting for termination by user.
Supports also blocking commands gdb and gdbtui to start a debugging
session in an active console.
Supports running gdbgui running a UI debugging session in a browser
window, using the active console for other commands, such as openocd
or monitor.
Supports combining the debug targets in one action list, such as
idf.py openocd gdbgui monitor
