TLS curves should be renamed to TLS groups and use preferred names

[lewart3]

TLS groups has superseded TLS curves:

• RFC 7919 (2016)
• RFC 8446 (2018)
• Transport Layer Security (TLS) Parameters

Therefore the Guidelines should use "TLS groups" instead of "TLS curves".

Also, SSL_CONF_cmd says:

The groups argument is a colon separated list of groups. The preferred names are those listed in the IANA TLS Supported Groups registry.

Therefore the TLS groups should be changed from:
    X25519MLKEM768, X25519, prime256v1, secp384r1
to:
    X25519MLKEM768, x25519, secp256r1, secp384r1