Add SLH-DSA signing.

Also updated function comments.

Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25882)

util/perl/OpenSSL/paramnames.pm

@@ -486,6 +486,7 @@ my %params = (
     'SIGNATURE_PARAM_DETERMINISTIC' =>      "deterministic",
     'SIGNATURE_PARAM_MU' =>                 "mu", # int
     'SIGNATURE_PARAM_TEST_ENTROPY' =>       "test-entropy",
+    'SIGNATURE_PARAM_ADD_RANDOM' =>         "additional-random",
 
 # Asym cipher parameters
     'ASYM_CIPHER_PARAM_DIGEST' =>                   '*PKEY_PARAM_DIGEST',