dnsdist: add lua support to limit TTL values of responses

[chbruyand]

Short description

This adds LimitTTLResponseAction(), SetMinTTLResponseAction() and SetMaxTTLResponseAction() to limit returned TTL values to given boundaries.

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]

Nice work! I think we need a few changes to keep the Lua FFI version fast, but nothing too complicated I hope.