Add dataset categories to data modules

[samet-akcay]

Description

• This PR adds list of categories to the corresponding datamodule script. Users will be able to list the available categories by importing CATEGORIES from the corresponding data module. For example, to get MVTec categories,

>>> from anomalib.data.mvtec import CATEGORIES
>>> CATEGORIES
('bottle', 'cable', 'capsule', 'carpet', 'grid', 'hazelnut', 'leather', 'metal_nut', 'pill', 'screw', 'tile', 'toothbrush', 'transistor', 'wood', 'zipper')

This would also be useful for benchmarking.

Changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which refactors the code base)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the pre-commit style and check guidelines of this project.
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• I have added a summary of my changes to the CHANGELOG (not for minor changes, docs and tests).