New Package support and removal of vulnerable Newtonsoft packages

[RocktimeLtd]

What problem does the pull request solve?

It allows support of new Newtonsoft and JWT packages. It drops support of vulnerable Newtonsoft packages Updated Unit tests so they support the new version of NUnit Added .NETFramework 4.8 Updated test packages and tests Merged in current origin/main

Checklist

• [x] I’ve used the pull request template
• [x] I’ve written unit tests for these changes
• [ ] I’ve updated the documentation in
  • [ ] notifications-tech-docs repository
  • [ ] CHANGELOG.md
• [ x] I’ve bumped the version number (in src/GovukNotify/GovukNotify.csproj)

[RocktimeLtd]

I have added the latest updates ready for merging