minor change to configuration.py

Summary

This MR introduces the following changes

• change if statement in preprocessing tools, to check if file exists

Relates to the following issues

• direct string comparison doesn't catch identical paths if / is repeated, e.g. 'samples//scale_dict.json' != 'samples/scale_dict.json', but both are pointing to the same file.

Conformity

• Changelog entry
• Documentation
• Development guidelines
• Style guides