Is your feature request related to a problem? Please describe.
I have number of custom extensions in spec file. Each extension field is named with x-* naming convention.

Describe the solution you'd like
I would like have option to provide list of field names, JSONPaths or some other way to express predicate specifying which things should be ignored during diffing. oasdiff diff has --exclude-elements option that allows to skip some predefined fields like description, examples. New option could be generalization of this option.

Describe alternatives you've considered
I could try to filter detected changes in oasdiff output, but returned JSON is
very complicated (it's like 20 nested objects), so it's not easy to
process.