[3.14] gh-142533: Document CRLF injection vulnerabilities in http.server doc (GH-143395) (#148020)

gh-142533: Document CRLF injection vulnerabilities in http.server doc (GH-143395)
(cherry picked from commit 617f4cc1c2605b86b4833450253c3599b61d6638)

Co-authored-by: Tadej Magajna <tmagajna@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>