knownhosts: Introduced ssh_known_hosts_get_algorithms_names()
The added internal function obtain a newly allocated string containing a
list of the signature types that can be generated by the keys present in
the known_hosts files, separated by commas.
Signed-off-by: Anderson Toshiyuki Sasaki <email@example.com>
Reviewed-by: Jakub Jelen <firstname.lastname@example.org>
(cherry picked from commit 65a38759ca872e8bec0158ab3676e74b6afd336f)