Document HttpClient migration from HttpWebRequest/ServicePoint(Manager)

[karelz]

HttpWebRequest API	HttpClient API
Accept
Address
AllowAutoRedirect
(TODO: add more)
ServicePoint API	HttpClient API
(TODO: add more)
ServicePointManager API	HttpClient API
(TODO: add more)

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Issue Details

---

HttpWebRequest API	HttpClient API
Accept
Address
AllowAutoRedirect
(TODO: add more)
ServicePoint API	HttpClient API
(TODO: add more)
ServicePointManager API	HttpClient API
(TODO: add more)

Author:	karelz
Assignees:	-
Labels:	documentation, area-System.Net.Http
Milestone:	9.0.0