smtpsrv: Disable TLS session tickets to work around Microsoft problems

Microsoft SMTP servers have a bug that prevents them from successfully
establishing a TLS connection against modern Go TLS servers, and some
OpenSSL versions. It also doesn't fall back to plain-text, so this has
been causing deliverablity issues.

The problem started by the end of 2024 and it's still not fixed.

Unfortunately, because they're quite a big provider and are not fixing
their problem, it is worth to do a server-side workaround.

This patch implements that workaround: it disables TLS session tickets.

There is no security impact for doing so, and there is a small
performance penalty which is likely to be insignificant for chasquid's
main use cases.

This workaround should be removed once Microsoft fixes their problem.

We are going to make a 1.15.1 release for this, which this patch also
documents.

Thanks to Michael (l6d-dev@github) for reporting this issue and
suggesting this workaround!

See https://github.com/albertito/chasquid/issues/64 and
https://github.com/golang/go/issues/70232 for more details.

docs/relnotes.md

@@ -11,6 +11,16 @@ noting backward-incompatible changes or known security issues.
 - Log how many things were loaded for each domain.
 - Add fail2ban filter configuration example.
 
+### 1.15.1 (2025-03-30)
+
+Implement a workaround for a Microsoft bug in TLS session ticket handling,
+that is causing deliverability issues, and they are being too slow at fixing.
+
+See this [chasquid issue](https://github.com/albertito/chasquid/issues/64),
+this [Go issue](https://github.com/golang/go/issues/70232) and this
+[Postfix thread](https://www.mail-archive.com/postfix-users@postfix.org/msg104308.html)
+for more details.
+
 
 ## 1.14.0 (2024-04-21)