API for loading a provider #567

In previous versions, I was able to load an engine using OpenSSL::Engine.load() and OpenSSL::Engine.by_id("pkcs11"). Now that engine support has been removed, I've installed a matching OpenSSL 3.0 provider, but there seems to be no Ruby equivalent for openssl pkey -provider pkcs11 (I believe that's OSSL_PROVIDER_load()).