Upgrade Blazor app to .net 8

[dynamictulip]

We really should migrate to .NET 8 before LTS ends on .NET 6.

Tried to do this earlier in the year but there was an issue with a core nuget package (Fluxor) not working with .NET 8. They have some issues open around .NET 8 compatibility which may help to diagnose/fix the problems

[dynamictulip]

We've decided to put this work on hold for the moment - MudBlazor and/or Fluxor are unhappy so we'll try again when we've a little more time to dedicate to it.