SSL: external groups support in $ssl_curve and $ssl_curves.

SSL: external groups support in $ssl_curve and $ssl_curves.

Starting with OpenSSL 3.0, groups may be added externally with pluggable
KEM providers.  Using SSL_get_negotiated_group(), which makes lookup in a
static table with known groups, doesn't allow to list such groups by names
leaving them in hex.  Adding X25519MLKEM768 to the default group list in
OpenSSL 3.5 made this problem more visible.  SSL_get0_group_name() and,
apparently, SSL_group_to_name() allow to resolve such provider-implemented
groups, which is also "generally preferred" over SSL_get_negotiated_group()
as documented in OpenSSL git commit 93d4f6133f.

This change makes external groups listing by name using SSL_group_to_name()
available since OpenSSL 3.0.  To preserve "prime256v1" naming for the group
0x0017, and to avoid breaking BoringSSL and older OpenSSL versions support,
it is used supplementary for a group that appears to be unknown.

See https://github.com/openssl/openssl/issues/27137 for related discussion.