mbedtls_ssl_session::ticket_creation_time field

When a ticket is created by a TLS server as part of an established TLS session, the ticket creation time may need to be saved for the ticket module to be able to check the ticket age when the ticket is used. That's the purpose of this field. Before creating a new ticket, an Mbed TLS server set this field with its current time in milliseconds. This time may then be saved in the session ticket data by the session ticket writing function and recovered by the ticket parsing function later when the ticket is used. The ticket module may then use this time to compute the ticket age and determine if it has expired or not. The Mbed TLS implementations of the session ticket writing and parsing functions save and retrieve the ticket creation time as part of the session ticket data. The session ticket parsing function relies on the mbedtls_ssl_session_get_ticket_creation_time() API to get the ticket creation time from the session ticket data.