doc: ref OpenSSL legacy provider from crypto docs

This adds a link to the --openssl-legacy-provider flag to the
"Support for weak or compromised algorithms" section.

PR-URL: https://github.com/nodejs/node/pull/40593
Refs: https://github.com/nodejs/node/pull/40478


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Voltrex <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Beth Griggs <bgriggs@redhat.com>