dnsdist: Implement Lua custom web endpoints

[rgacogne]

Short description

Closes #9120.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[rgacogne]

Weird test-auth-regress-bind error in bind-dnssec-nsec3-both, during verify-dnssec-zone:

Nov 06 10:40:12 AXFR of domain 'tsig.com' allowed: client IP 127.0.0.1:46172 is in allow-axfr-ips
AXFR failed.
Syntax error, could not parse the RR's TTL at 0
Nov 06 10:40:12 Received serial number updates for 1 zone, had 0 timeouts

[wojas]

Nice!