MINOR: cfgparse/http: add a simple parser for new section "http-fingerprint"

MINOR: cfgparse/http: add a simple parser for new section "http-fingerprint"

Just like the resolvers parser, this is a whole section parser. It handles
both the http-fingerprint keyword that creates the section, and all
registered hardening options supported there. The format is:

    http-fingerprint <name> [from <origin>]
         <option> [on|off]
         ...

A section may only be declared once, and the origin must already exist if
mentioned (like with defaults). Like with http-violations, keywords are
resolved using fuzzy matching so that an approaching name will suggest
the correct one.

For now, no keywords beyond "all" are declared, and nothing is done with
these sections.