Enable ARC_Support

[kingjamez]

It would be super if G2/G3 (ARC_Support) were enabled so we could use ARC_WELDER plugin in OctoPrint, or the native cura arc outputs. This simplifies g-code and smooths printer motion for no downside. As far as I can tell this must be enabled in configuration_adv.h .

[Ukchris79]

I thought it was enabled, I have been using the octoprint plugin for the last two weeks and converting the files, so far no issues