AP job-fails on EXR files containing channels other than RGBA

Describe the bug In the file https://github.com/o3de/o3de/blob/main/Gems/Atom/Asset/ImageProcessingAtom/Code/Source/ImageLoader/ExrLoader.cpp (Development branch as well), RGBA channel structure is hard-coded as if there can't be any else channel. But we know .exr files do come with other channels such as Y, Z etc. Implies that, maybe the whole .exr handling structure is (sort of) flawed, since for example even with a "Z channel only" texture re-exported to RGB might gonna cost 3x memory usage.

Assets required rock_face_04_1k [credit - Polyhaven].zip

Steps to reproduce

1. Have the provided asset files in the project folder. [Any folder that AP scans]
2. Now get the o3de editor started with the chosen project.
3. At this point, AP should fail to cache a few textures (rough, ao, disp) provided in the .zip file.

Expected behavior These single channel textures should've been processed just like other multichannel textures.

Actual behavior AP fails to process specifically the single channel textures (textures that don't have standard RGBA channels).

Screenshots/Video

Found in Branch Confirmed to be found in main & development branch

Commit ID from o3de/o3de Repository Commit id is not applicable in this case, since I downloaded o3de as an offline installer (v26.05.0) from https://o3debinaries.org/download/windows.html

Desktop/Device:

• Device: Acer Aspire A315-58
• OS: Windows
• Version 11
• CPU 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz (2.42 GHz)
• GPU Intel(R) Iris(R) Xe Graphics (128 MB)
• Memory 20GB

Additional context None.