Improve routes

[rayrfan]

Summary

Consider to make routes more centralized and re-used better instead of hardcoding them at different places. Particularly the following two areas worth looking at

• Startup.cs: delegate endpoint routings to different parts of the application
• Blazor theme: page components current have routes hardcoded on them. Note: if variables are needed on the page directive attribute directive with the Route attribute can be used instead (see Support variable for Blazor @page directive declaration dotnet/aspnetcore#25589)