Update to .net 7

[Trigun27]

Thanks to @mlaily, i just updated PR to .net 7

Summary of the changes (also see commit list):

• Updated to .NET 7.0 and Giraffe 6

• Extract the views to a C# project so we get full VS support in .cshtml files

  • This is probably the most controversial change of this PR. It seems Visual Studio does not completely support cshtml files in fsproj project, and the intellisense does not work. This considerably reduces the usefulness of Razor views.

  • It complexifies the sample a bit, but this seems like a more realistic usage and I think the tradeoff is worth it.

• Other minor fixes and improvements.

[Trigun27]

@TheAngryByrd hi! Can you review PR? Thanks