Improve the documentation on TLS record compression

Improve the documentation on TLS record compression

TLS record compression is off by default. Even if you switch it on, it
cannot be used at security level 2 which is the default in OpenSSL 3.2 and
above. Update the docs to point this out.

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23104)