Enable on-the-fly response compression for WebDAV when the client sends
Accept-Encoding and the response content type is suitable for
compression.
This adds compression for the WebDAV responses that benefit most in
practice, notably PROPFIND XML responses and text file downloads.
I tested this with Cyberduck, which sends
`Accept-Encoding: gzip,deflate` and accepted the compressed responses.
Range requests are explicitly left uncompressed.
Fixes#5777
Leon BrocardandGitHub
6f1678419f