[Review request] Added board config for Mellow Fly E3 v2

Hi,

I recently converted my old Tiertime Up Mini to klipper using a Team Gloomy Mellow Fly E3 v2. There is very few information available for this board on running Klipper and required some research and a lot of testing.

The printer has about 5kg of PLA and 3kg of ABS printing now on this configuration, working like a charm.

I was wondering if a reviewer would like to take the time to review this PR (#6682) to help other people using this board in their builds.

I will add a self review in the next couple of days and a full writeup of the conversion in the near future here

I thank you beforehand