tls: get the local certificate after tls handshake

Add an API to get the local certificate chosen during TLS handshake from
the SSL context.

Fix: https://github.com/nodejs/node/issues/24095

PR-URL: https://github.com/nodejs/node/pull/24261
Fixes: https://github.com/nodejs/node/issues/24095


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>