doc: Document properties param for Argon2 KDF

The Argon2 KDF uses OSSL_KDF_PARAM_PROPERTIES to fetch implementations
of blake2bmac and blake2b512 if ctx->mac and ctx->md are NULL. This
isn't documented in the manpage, so users that might, for example, want
to fetch an instance of Argon2 with the -fips property query to obtain
a working Argon2 KDF even though the default property query requires
fips=yes are left wondering why this fails.

Fortunately, EVP_KDF(3)/PARAMETERS already explains what the properties
are used for, so we really just need to add a single line.

Signed-off-by: Clemens Lang <cllang@redhat.com>

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25306)

(cherry picked from commit 6772c2ab)