MEDIUM: http: move reqadd after execution of http_request redirect

MEDIUM: http: move reqadd after execution of http_request redirect

We still have a plate of spaghetti in the request processing rules.
All http-request rules are executed at once, then some responses are
built interlaced with other rules that used to be there in the past.
Here, reqadd is executed after an http-req redirect rule is *decided*,
but before it is *executed*.

So let's match the doc and config checks, to put the redirect actually
before the reqadd completely.