feat: add OpenEXR to supported list of image formats

[stackcoder]

Description

This PR adds OpenEXR to the list of supported image formats.

OpenEXR is a high–dynamic‑range, multi‑channel raster file format released as an open standard under a free software license similar to the BSD license. Using OpenEXR instead of TIFF can save disk space, especially when using lossless compression.

How Has This Been Tested?

1. Go to openexr.com and download a test image.
2. Rename the downloaded image to an already supported file extension (e.g., .raw).
3. Upload the renamed image to immich.
4. The image is displayed correctly by immich.

Because of this, I assume the underlying tech stack already supports OpenEXR and it is only missing from the supported file formats list.

Checklist:

• I have carefully read CONTRIBUTING.md
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
  Note: Could be added to supported-formats.md, the list already seems to be not complete by intent.
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

None used. Just followed the link provided by docs to the code.

[github-actions]

This PR has been automatically closed as the description doesn't follow our template. After you edit it to match the template, the PR will automatically be reopened.

[meesfrensel]

Thanks for the PR. Please take a look at #27963 to see where else to add the format.