Fix for #104, adding support for mounted apps

[goodwillcoding]

[goodwillcoding]

@zupo this is the fix I mentioned in #104 ... let me know if it looks ok to you and if you'd want it and I'll add tests

[zupo]

Can you please add a functional test for this?

[goodwillcoding]

Hi @zupo. I cleaned up the fix and updated the existing test for test_relative_app_request which tests path_pattern and it looks like that's the only test that needed to be done.

The PR checks above fail on pyupgrade run and I have not been able to reproduce that locally either via pyupgrade or pre-commit run. Not sure what to do there.

[zupo]

The PR checks above fail on pyupgrade run and I have not been able to reproduce that locally either via pyupgrade or pre-commit run. Not sure what to do there.

I'll have a look.

[mmerickel]

Without realizing this PR was here I think I just reimplemented the same fix that @goodwillcoding had done in this PR over at https://github.com/Pylons/pyramid_openapi3/pull/263.

Mine is slightly different in that I didn't use self.request.path because the existing self.request.path_info is properly relative to script_name so you can just add script_name to everything which I think is simpler.