exr: add multi-layer image for oiio test suite

[mugulmd]

Description

Add a simple EXR image with multiple channel-name-based layers for testing oiiotool's new --layersplit command, introduced in this PR: AcademySoftwareFoundation/OpenImageIO#4591

This image was generated with oiiotool, following the command line suggested in this comment: AcademySoftwareFoundation/OpenImageIO#4546 (comment)

[lgritz]

It LGTM, but usually OpenImageIO-images is for very large files or rarely needed file formats, to avoid bloating the main OpenImageIO repo with items that aren't strictly necessary to build for most users. At a mere 672 bytes, should example this just be directly checked into the main repo in the src subdirectory of whatever test you will use it for? Or even create it on the fly with oiiotool as part of that test, with no permanent version being checked in anywhere?

[mugulmd]

It LGTM, but usually OpenImageIO-images is for very large files or rarely needed file formats, to avoid bloating the main OpenImageIO repo with items that aren't strictly necessary to build for most users. At a mere 672 bytes, should example this just be directly checked into the main repo in the src subdirectory of whatever test you will use it for? Or even create it on the fly with oiiotool as part of that test, with no permanent version being checked in anywhere?

Ah right that makes sense ! We can definitely put it directly in the oiio PR, that makes one less PR :)