net/haproxy: upgrade to HAProxy 3.2 release series

[fraenki]

Scheduled for inclusion in OPNsense 26.1 or 26.1.1 (no promises!).

HAProxy 3.2 and the short-lived 3.1 release series introduced noteworthy enhancements:

• HTTP/2 performance improvements (especially for POST requests)
• Automatic CPU binding improves overall performance (mostly for massively multi-core systems)

As usual, a number of tasks need to be completed:

• Add HAProxy 3.2 package
• Check for removed features / incompatible changes
• Replace deprecated functionality
• Perform a set of tests
• Document known issues (nothing found so far)
• Update documentation URLs to point to 3.2 docs
• Add support for new config options (OPTIONAL)

More details:
https://www.haproxy.com/blog/announcing-haproxy-3-1
https://www.haproxy.com/blog/announcing-haproxy-3-2

[fraenki]

Done via #5101.

[fraenki]

Upgrade is probably blocked by haproxy/haproxy#3254. I'll handle this in #5101.