Create migration guide for ASP.NET applications

[TimothyMothra]

This PR adds a guide for migrating ASP.NET applications to OpenTelemetry.
Our team decided to start with ASP.NET.

Notes

• We don't have a reputable example of configuring ILogger to ASP.NET applications.
• All the steps in this doc are "Step 1". This is to make my life easier when making large changes to this doc. We can fix this before publishing.

[cijothomas]

https://learn.microsoft.com/en-us/azure/azure-monitor/app/asp-net#how-can-i-uninstall-the-sdk

[TimothyMothra]

Thanks for sharing. I'm trying to reference existing docs as much as possible, but I didn't find this doc.
Regrettably, this doc is horribly out of date. But a number of our users are on older versions of our SDK where this might still be relevant. Let me think about how to handle this.

[TimothyMothra]

Closing. will keep rough draft internal until ready to publish