Feature Request: Support printing from virtual SD card

[potchin]

I've moved to using the virtual SD card feature of klipper to get some performance improvements. I would be very useful to be able to load and start prints via octoprint in a similar way to what can be done in the native octoprint UI.

The list of files could either be populated by an M20 command or alternatively the local filesystem could be read after reading the directory location from the klipper config.

To start the print is simply an M23 filename.gcode then M24..

https://github.com/KevinOConnor/klipper/blob/e26d1a356708b3702c91a86ff37f3c5c615941c9/docs/G-Codes.md#g-code-sd-card-commands