Added Include note about class being obsolete

[lorieide]

Summary

Describe your changes here.

Fixes #Issue_Number (if available)

[gewarren]

@lorieide What's the motivation behind this PR?

[lorieide]

@lorieide What's the motivation behind this PR?

@gewarren Sure. I've been assigned this GitHub issue to resolve MicrosoftDocs/azure-docs#111552

[lorieide]

@gewarren Here's what I found:
The .NET WebRequest and HttpWebRequest classes are indeed considered obsolete and are recommended to be replaced with HttpClient. This is in line with modern development practices and the evolution of the .NET framework. Specifically, as per the Microsoft documentation, starting from .NET 5+, it is advised to use HttpClient instead of WebRequest, HttpWebRequest, ServicePoint, and WebClient.
I validated this information is correct as all of these topics have a scattered Important note about this development.
I recommend adding a warning note as an include below to all of the topics in the WebRequest, ServicePoint, WebClient, and HttpWebRequest Class topics.

[gewarren]

@lorieide Ahh, okay. Currently, if a .NET API is marked with the ObsoleteAttribute, for example, WebRequest.Create, then the API reference docs automatically show the CAUTION block with the text from the ObsoleteAttribute. So that's why you see the info on some APIs and not others. There's also a work item to propagate the obsolete warning to all members of a type that's marked obsolete (although I don't think that applies to any of these 4 System.Net types unfortunately).

Related to #6867.

[learn-build-service-prod]

Learn Build status updates of commit 409844e:

✅ Validation status: passed

File	Status	Preview URL	Details
includes/web-request-obsolete.md	✅Succeeded	View
xml/System.Net/HttpWebRequest.xml	✅Succeeded	View
xml/System.Net/ServicePoint.xml	✅Succeeded	View
xml/System.Net/WebClient.xml	✅Succeeded	View
xml/System.Net/WebRequest.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

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[MihaZupan]

FYI ServicePointManager was just marked as obsolete in dotnet/runtime#103456.
And while types like ServicePoint/WebRequest aren't explicitly marked as obsolete, they effectively are since all the ways to obtain their instances (ServicePointManager.FindServicePoint, WebRequest.Create) are obsolete.

[learn-build-service-prod]

Learn Build status updates of commit f9a8675:

✅ Validation status: passed

File	Status	Preview URL	Details
includes/web-request-obsolete.md	✅Succeeded	View
xml/System.Net/HttpWebRequest.xml	✅Succeeded	View
xml/System.Net/ServicePoint.xml	✅Succeeded	View
xml/System.Net/WebClient.xml	✅Succeeded	View
xml/System.Net/WebRequest.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel