Add the engineering plate from Bambu#611

Like the title says, I cannot seem to pick any other plate except the default textured pei plate.

We do have the engieering one. Chances are you have maybe disabled all other bed types in settings?
https://simplyprint.io/panel/settings/general

“Visible bed types”.

If you believe there’s a bug, reach out to support, but closing as this is a feature.