tls: support changing credentials dynamically

This commit adds a setSecureContext() method to TLS servers. In
order to maintain backwards compatibility, the method takes the
options needed to create a new SecureContext, rather than an
instance of SecureContext.

Fixes: https://github.com/nodejs/node/issues/4464
Refs: https://github.com/nodejs/node/issues/10349
Refs: https://github.com/nodejs/help/issues/603
Refs: https://github.com/nodejs/node/issues/15115
PR-URL: https://github.com/nodejs/node/pull/23644


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>