palette2: Add support for P2 devices (#4057)

Module which bring support for P2 devices running in connected mode. This enables using a Palette2 directly with Klippy without Octoprint, or without Palette2 plugins for Octoprint which are not functional out of the box with Klipper.

Signed-off-by: Clifford Roche <clifford.roche@gmail.com>

docs/Config_Reference.md

@@ -3750,3 +3750,37 @@ I2C bus.
 #   On some micro-controllers changing this value has no effect. The
 #   default is 100000.
 ```
+
+# Other Custom Modules
+
+## [palette2]
+
+Palette 2 multimaterial support - provides a tighter integration
+supporting Palette 2 devices in connected mode.
+
+This modules also requires `[virtual_sdcard]` and `[pause_resume]`
+for full functionality.
+
+If you use this module, do not use the Palette 2 plugin for
+Octoprint as they will conflict, and 1 will fail to initialize
+properly likely aborting your print.
+
+If you use Octoprint and stream gcode over the serial port instead of
+printing from virtual_sd, then remo **M1** and **M0** from *Pausing commands*
+in *Settings > Serial Connection > Firmware & protocol* will prevent
+the need to start print on the Palette 2 and unpausing in Octoprint
+for your print to begin.
+
+```
+[palette2]
+serial:
+#   The serial port to connect to the Palette 2.
+#baud: 250000
+#   The baud rate to use. The default is 250000.
+#feedrate_splice: 0.8
+#   The feedrate to use when splicing, default is 0.8
+#feedrate_normal: 1.0
+#   The feedrate to use after splicing, default is 1.0
+#auto_load_speed: 2
+#   Extrude feedrate when autoloading, default is 2 (mm/s)
+```

docs/G-Codes.md

@@ -760,3 +760,27 @@ is enabled (also see the
   defaults to the current time in "YYYYMMDD_HHMMSS" format. Note that
   the suggested input shaper parameters can be persisted in the config
   by issuing `SAVE_CONFIG` command.
+
+## Palette 2 Commands
+
+The following command is available when the
+[palette2 config section](Config_Reference.md#palette2)
+is enabled:
+- `PALETTE_CONNECT`: This command initializes the connection with
+  the Palette 2.
+- `PALETTE_DISCONNECT`: This command disconnects from the Palette 2.
+- `PALETTE_CLEAR`: This command instructs the Palette 2 to clear all of the
+  input and output paths of filament.
+- `PALETTE_CUT`: This command instructs the Palette 2 to cut the filament
+  currently loaded in the splice core.
+- `PALETTE_SMART_LOAD`: This command start the smart load sequence on the
+  Palette 2. Filament is loaded automatically by extruding it the distance
+  calibrated on the device for the printer, and instructs the Palette 2
+  once the loading has been completed. This command is the same as pressing
+  **Smart Load** directly on the Palette 2 screen after the filament load
+  is complete.
+
+Palette prints work by embedding special OCodes (Omega Codes)
+in the GCode file:
+- `O1`...`O32`: These codes are read from the GCode stream and processed
+  by this module and passed to the Palette 2 device.