Summary

Closes #4936

I also took the opportunity to refactor the methods that we use for auto search and loading user configuration:

• the auto search now works only for one single file, instead of accepting multiple files. This reduces the cognitive complexity, it doesn't raise diagnostic and we use a single loop,
• the logic we had in the auto search regarding "should_emit_error" was introduced only when searching for configuration files, however we raise an error only when the user provide --config-path, which doesn't trigger an auto-search.
• the loading of user configuration has been moved into its own function with its own logic, which must raise an error if we can't find a configuration file
• I refactored load_editorconfig and reduced its cognitive complexity. We now use a more functional approach to map the fields we need to validate.

Test Plan

Added new tests and updated the existing ones