[CTX] [ALL] header generation

add-[i][qr]head:name:body
add a header name:body to forwarded request/response message. Client's identity information can be inserted into body string with "%format" notation. If "i" is prefixed as "add-ihead:Pragma:no-cache", then the specified field with the body is added to the input to be interpreted by DeleGate as a HTTP header from the client or the server.

Example: