Add troubleshooting information

### Description

Verbatim from the feedback control:
> Please document HOW, WHEN and WHY requests from an .http file can file and, most importantly, HOW TO TELL WHAT WENT WRONG. A stupid tooltip that reads "Last request had errors. Click to send a new request" is NOT helpful. Nothing appears in any output window detailing the error, and the HTTP endpoint was never hit. I'd provide more details through the Visual Studio feedback mechanism, but that hasn't worked for me FOR YEARS due to the chaos that is Microsoft Federated identity.

### Page URL

https://learn.microsoft.com/en-us/aspnet/core/test/http-files?view=aspnetcore-8.0

### Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/test/http-files.md

### Document ID

26f1374f-556a-35fc-cc42-b8911746db80

### Article author

@tdykstra