MEDIUM: http/hardening: implement hardening "reject-ctl-in-header-trailer"

MEDIUM: http/hardening: implement hardening "reject-ctl-in-header-trailer"

Rejects requests and responses which contain control characters in
their header or trailer field values (codes 0-8,10-31,127). These ones
are forbidden but have long experienced a certain tolerance among
implementations, which has encouraged some rare applications to use
them as record delimiters for example. No standard component produces
them on the public internet, except attacks. By default, HAProxy only
blocks the strictly required ones (0,10,13) and lets other ones pass,
which can make certain backend applications trigger connection errors.
As such, it is both safe and recommended to block them on public facing
listeners. See also the has_ctl() converter used for detecting them.