Set HTTP upgrade headers when hijacking connection

Signed-off-by: Jean-Tiare Le Bigot <jt@yadutaf.fr>
Set HTTP upgrade header only when requested by client

Signed-off-by: Jean-Tiare Le Bigot <jt@yadutaf.fr>
Update connection hijacking documentation with HTTP Upgrade Headers

Signed-off-by: Jean-Tiare Le Bigot <jt@yadutaf.fr>
Merge pull request #9652 from yadutaf/master

Set HTTP upgrade headers when hijacking connection