[ADD] .NET 8 support for the Auth0 Blazor WebAssembly template

[RobinS-S]

Description

The Blazor WebAssembly .NET template for Auth0 supports .NET 7. As .NET 8 has been released, I added support for .NET 8.

Testing

You can test this PR by locally installing the template and creating a project for both .NET 7 and .NET 8. Run and test the application. There is no automated testing available.

Checklist

• [x] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [x] All active GitHub checks for tests, formatting, and security are passing
• [x] The correct base branch is being used, if not the default branch

[andychiare]

Hey @RobinS-S, thank you so much for your contribution. In the next few days I'll test the template and possibly merge your PR