net/haproxy: support built-in WAIT_END acl rule and/or wait_end condition

[wjl]

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Is your feature request related to a problem? Please describe.

I've switched a firewall machine from a custom setup to OPNsense, and am porting my HAProxy configuration from a file to OPNsense's GUI. One missing thing I've found was there was no good way to write this succinctly, and no way to do it without an option pass-through that I could find:

tcp-request content reject if WAIT_END

The workaround I had to use was to:

1. Make a condition "wait_ended" with an option pass-through of "wait_end".
2. Make a rule "reject-on-timeout" with the "wait_ended" condition in a rule with "tcp-request content reject".

Describe the solution you'd like

This works once I figured it out, but it was pretty round-about, especially since HAProxy already has WAIT_END as a built-in acl and wait_end as a built-in conditional (which I've never otherwise used and I had to discover from the HAProxy docs while trying to make this work!). So ideally, I would have been able to:

• Make my "reject-on-timeout" rule with "tcp-request content reject" and the condition WAIT_END (built-in).
• Alternately, make my "wait_ended" condition with "wait_end" selected from the drop down, instead of using option pass-through.

Describe alternatives you've considered

There is no alternative that I'm aware of -- using an indirect condition with option pass-through was the only way I could figure out to make this work.

Additional context

The pattern of using inspect-delay followed by a WAIT_END is a pretty common pattern in HAProxy configs. For example, I use this when multiplexing SSH over both HTTP and HTTPS ports:

tcp-request inspect-delay 5s
tcp-request content accept           if is_ssh_payload
tcp-request content accept           if is_https_port is_https_proto
tcp-request content switch-mode http if is_http_port  is_http_proto
tcp-request content reject           if WAIT_END