Create GH actions release pipeline

[andrueastman]

This PR adds a GitHub action release pipeline to create a new package release with a StrongName.

The GH action:

• Builds and tests and does CodeQL analysis the library on pushes/PRs to the master branch
• Attempts to deploy the built nuget packages on pushes to master

Example run is at https://github.com/andrueastman/Tavis.UriTemplates/actions/runs/2918361942

Other changes include :-

• Adds the UriTemplateKey.snk to enable strong name signing of the generated package
• Updates the library to only target netstandard2.0 as the other targets are out of support(version has already been major bumped according to latest release)
• Updates the csproj to support SourceLink to enable symbol publishing for developers to be able to step into the code.
• Updates the Release notes file
• Updates the test project to target net6.0 as net5.0 is out of date

cc @darrelmiller