Enable image-level normalization flag

[ashwinvaidya17]

📝 Description

• Partially restores https://github.com/openvinotoolkit/anomalib/pull/1303
• The original PR set this flag to true automatically when Normalisation Mode was set to None. But since we pass the visualisers to the Engine, it now needs to be set by the user.

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• [x] 🐞 Bug fix (non-breaking change which fixes an issue)
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• [ ] 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] 📚 Documentation update
• [ ] 🔒 Security update

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