doc: clarify algorithm discovery in openssl-genpkey.pod.in

doc: clarify algorithm discovery in openssl-genpkey.pod.in

Add a reference to 'openssl list -public-key-algorithms' in the
-algorithm description to improve discoverability and long term
consistency. Documentation only change.

Add clarification for how to select the naming output in the correct spot.

Reviewed-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
MergeDate: Sun May 10 23:59:03 2026
(Merged from https://github.com/openssl/openssl/pull/30556)