docs: configmode: mention gluon-enter-setup-mode

The command was introduced in v2022.1 with #2459.

Co-authored-by: Jan-Niklas Burfeind <github@aiyionpri.me>
(cherry picked from commit b4f174a4)

docs/features/configmode.rst

@@ -18,6 +18,9 @@ Config Mode by pressing and holding the RESET/WPS/DECT button for about three
 seconds. The device should reboot (all LEDs will turn off briefly) and
 Config Mode will be available.
 
+If you have access to the console of the node, there is the
+``gluon-enter-setup-mode`` command, which reboots a node into Config Mode.
+
 
 Port Configuration
 ------------------