Duo-universal

Changes:
- Improve the source distribution process to ensure all required files are present
- Include a Software Bill of Materials (SBOM) in a release
- Add support for an HTTP proxy
- Add support for an OIDC `nonce`
- Allow customization of the JWT expiration window
- Drop Python 3.6 support. add Python 3.11 support

Release notes:
- Improved the way we include all required files in the source distribution, thanks to https://github.com/kmosiejczuk

Release notes:
- Improved the example application with customizable certificates and configuration name
- Resolved a distribution issue where the tarball artifact was missing a file

- Dropped Python 2 support
- Bug fix in the demo

Features
- Enabled toggling of whether the client will use `code` or `duo_code` for the OIDC authorization code parameter name

Bug Fixes
- Minor fixes to demo application

Other Changes
- Removed testing with Python 3.5
- Added testing with Python 3.9
- Adjusted requirements to allow for more version flexibility
- Updated documentation link