Remove hardcoded values from matchers and allow specifying example values

[sergeyklay]

In comparison to other languages that let you specify the example value, pact-python currently has hardcoded values in all (or almost all) matchers. This issue needs to be addressed while preserving backward compatibility.

Removing hardcoded values and allowing users to specify example values would enhance the flexibility and usability of the matchers. A solution should be implemented that maintains the existing functionality for those who rely on it, while introducing the option to provide custom example values where necessary.