Rendered PNGs should "bleed color to alpha"

[brecert]

Currently most (if not all) of the rendered PNGs appear to have black set as the primary color of the alpha. This causes a noticeable darker outline on many of the flags, especially with generated mipmaps in resonite. (no image provided)

The rendered PNGs should have their texture padded into the alpha (the "bleed color to alpha" operation in Resonite's case) to avoid this.

[Frooxius]

This does get applied when we upload them to Resonite's standard assets. But we don't have that pipeline setup to run through this repo.