Migration FAQ for ARR

[Tratcher]

Some FAQ's from customers coming from ARR:

preserveHostHeader - https://microsoft.github.io/reverse-proxy/articles/transforms.html#requestheaderoriginalhost

reverseRewriteHostInResponseHeaders - not directly supported - #1548

arrResponseHeader - N/A - YARP doesn't add an X-Powered-By header

minResponseBuffer - not configurable -

reverse-proxy/src/ReverseProxy/Forwarder/StreamCopier.cs

Lines 20 to 21 in 25c9ff2

	// Based on performance investigations, see https://github.com/microsoft/reverse-proxy/pull/330#issuecomment-758851852.
	private const int DefaultBufferSize = 65536;

minFreeThreads - https://learn.microsoft.com/en-us/dotnet/api/system.threading.threadpool.setminthreads?view=net-7.0

minLocalRequestFreeThreads - N/A

relaxedUrlToFileSystemMapping - N/A

executionTimeout - ActivityTimeout is the closest approximation - https://microsoft.github.io/reverse-proxy/articles/http-client-config.html#httprequest