MINOR: cli/http: add the "show http-hardening" CLI command

MINOR: cli/http: add the "show http-hardening" CLI command

Without argument, "show http-hardening" lists all known profiles, including
the implicit "untrusted" and "trusted" ones when they were not declared (they
are then marked "(implicit)"). With a profile name, it shows each known
single-bit hardening option of this profile, along with its number (bit
position plus 1), direction among "req", "res", "-" (for bidir) and the
status ("on" or "off"), so that it is easy to know what is enabled.
Keywords covering a set of options such as "all" are not shown.