Add import configuration for background roughness texture

- Introduced a new import file for the background roughness texture located at `sourceimages/background_txt_pbr/background_txt_roughness.png`.
- Configured texture compression settings and metadata for optimal performance.
- Set up dependencies and parameters for texture processing, including mipmap generation and channel remapping.

project.godot

@@ -164,4 +164,8 @@ common/enable_pause_aware_picking=true
 [rendering]
 
 textures/vram_compression/import_etc2_astc=true
+scaling_3d/mode=5
+scaling_3d/mode.ios=5
+scaling_3d/mode.macos=5
+scaling_3d/scale=0.33330000000000004
 environment/defaults/default_environment="res://default_env.tres"