Improve HttpClient exception docs (#11103)

- For each HttpClient method, list all main cases where an `HttpRequestException` might be thrown.
- Add missing exception docs for `PatchAsync`.
- Extend remarks for `EnsureSuccessStatusCode`.
- Add remarks for `Get(ByteArray|Stream|String)Async`, calling out that in some cases manual status code validation might be a better option

Author: antonfirsov