Add `Web.config` example to ASP.NET Quick Start guide

[Flash0ver]

Description

We do document the usage of appsettings.json for ASP.NET Core. But we do not document the usage of Web.config for ASP.NET (.NET Framework).

Let's add a basic example that at least configures the Data Source Name (DSN).

Based on sentry-docs user feedback (see Linear-issue below).

[linear[bot]]

NET-543