🔨 Update lightning inference

[djdameln]

📝 Description

This PR adds some minor modifications to the lightning inference:

• Adds two properties (checkpoint_callback and best_model_path) to the engine that help with retrieving the path of the saved checkpoint.
• Adds data_path argument to engine.predict to allow passing the path to a (folder of) image(s) directly to the entrypoint. This way the user does not need to create a PredictDataset.
• Updates the CLI to reflect the API changes.

✨ Changes

Select what type of change your PR is:

• 🐞 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)
• 📚 Documentation update
• 🔒 Security update

✅ Checklist

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• 📋 I have summarized my changes in the CHANGELOG and followed the guidelines for my type of change (skip for minor changes, documentation updates, and test enhancements).
• 📚 I have made the necessary updates to the documentation (if applicable).
• 🧪 I have written tests that support my changes and prove that my fix is effective or my feature works (if applicable).

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[ashwinvaidya17]

Thanks! Looks good to me

[samet-akcay]

lgtm,thanks