Fix T63635: Node Wrangler does not set relative paths for images using Add...

Fix T63635: Node Wrangler does not set relative paths for images using Add Texture Setup (Ctrl+Shift+T)

Using absolute paths for texture images break materials if the project is moved to another location or computer. Relative paths are also the default option in Image Texture Node's file view.

This adds a toggle to use relative paths when adding a texture setup for Principled BSDF. The option is selected by default to match Image Texture Node's behavior.

Tested on Blender v2.81.16 (Windows)

Reviewed By: lichtwerk, mont29

Maniphest Tasks: T63635

Differential Revision: https://developer.blender.org/D6756