Add { name: tls, version: <some_version> } support

[bneradt]

Currently, Proxy Verifier uses the generic openssl context creation API which negotiates the highest version of TLS agreed upon by both the Prover Verifier host and the peer. The version node, if specified in the YAML protocol:tls node, is ignored. It could be helpful for testing purposes to support parsing this node and negotiating that version of TLS in the handshake, both for the client via the session:protocol:tls:version node and for the server on the proxy-request:protocol:tls:version node.