dnsdist: Allow TTL alteration via Lua

[rgacogne]

Short description

Add AddLuaResponseAction(), identical to AddLuaAction() but for responses, and DNSResponse:editTTLs(func) to be able to edit response TTL froms Lua.
Closes #4707.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled and tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added regression tests