update to .net 5

[happy1836]

can update to .net 5 ,thanks

[JohnCampionJr]

Trying to figure out a way to do this myself, I created a repo with .NET 5 and fixed #1
I know I should've forked but I wanted to start with a fresh copy and only wanted path based multiple apps.

https://github.com/JohnCampionJr/Blazor5MultipleApps