crypto/tls: randomly generate ticket_age_add

crypto/tls: randomly generate ticket_age_add

As required by RFC 8446, section 4.6.1, ticket_age_add now holds a
random 32-bit value. Before this change, this value was always set
to 0.

This change also documents the reasoning for always setting
ticket_nonce to 0. The value ticket_nonce must be unique per
connection, but we only ever send one ticket per connection.

Fixes #52814
Fixes CVE-2022-30629

Change-Id: I6c2fc6ca0376b7b968abd59d6d3d3854c1ab68bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/405994
Reviewed-by: Tatiana Bradley <tatiana@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Run-TryBot: Tatiana Bradley <tatiana@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>