ASP.NET Core docs should use WebApplication.CreateBuilder

[jamescrosswell]

Description

The docs here for getting started:
https://docs.sentry.io/platforms/dotnet/guides/aspnetcore/configuration/options/

...currently describe how to configure Sentry using ASP.NET Core 2.x (WebHost.CreateDefaultBuilder) and ASP.NET Core 3.0 (Host.CreateDefaultBuilder) but not via the modern default for net6.0 and later (WebApplication.CreateBuilder).

We should keep up with the times in our docs and samples.

[linear]

NET-382 ASP.NET Core docs should use WebApplication.CreateBuilder