TLS 1.2 handshake compatibility

Some TLS servers, even though supporting TLS 1.3, require the client to send a non-empty session ticket, and other mechanisms specified in https://www.rfc-editor.org/rfc/rfc8446#appendix-D.4 . 

Embedded-tls should implement these in order to work with non-TLS 1.3 "middle boxes"