Add support for HEJ2K mime type (backport #2841)

[mergify]

See https://www.itu.int/rec/T-REC-T.815/en

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This is an automatic backport of pull request #2841 done by Mergify.

[mergify]

Cherry-pick of 5645fe6 has failed:

On branch mergify/bp/0.28.x/pr-2841
Your branch is up to date with 'origin/0.28.x'.

You are currently cherry-picking commit 5645fe6c8.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   test/data/Reagan.hej2
	new file:   test/data/test_reference_files/Reagan.hej2.out

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/bmffimage.cpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally