Reccomended usage of System.Net.Http should be noted

### Type of issue

Missing information

### Description

I've learned through a series of [stackoverflow posts](https://stackoverflow.com/questions/57803285/use-latest-version-of-system-net-http-in-net-framework) and [comments on GitHub](https://github.com/dotnet/runtime/issues/65005#issuecomment-1104956294) from maintainers of dotnet that we apparently should not be pulling `System.Net.Http` as a package from NuGET.

As this situation is tricky/difficult to follow and understand how you _could even use_ System.Net.Http without pulling it as a package, I feel it should be made much more clear:

1. Why the team supporting dotnet does not recommend using a package manager as you would for many other packages in an application
2. How users ought to make use of system packages like this (literally, the mechanism and what packages are included per framework should be simple to find)

I am having trouble finding an authoritative source for this recommendation, or confirmation on where system packages can come from if not from NuGET.

We ought to supply this information very clearly _on the page of every system package included with a framework_. It's tricky for me to figure out which package versions I can and can't use, what versions are available from different framework distributions, etc.

Please consider adding more information in the documentation for each given class.

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.net.http?view=net-9.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/ns-System.Net.Http.xml

### Document Version Independent Id

d487a3d2-e28c-fd3a-faaa-1e86c59c1720

### Platform Id

46900f01-fe7b-f84a-7237-cfdc169c043f

### Article author

@karelz