dnsdist: Implement tag-based routing, add missing LuaAction and LuaResponseAction

[rgacogne]

Short description

It is now possible to assign a tag and a value to a query with TagAction() and to match on this tag and value with TagRule(). Tags are passed along to response so it's possible to match a response based on a tag set while processing the query. TagResponseAction() can also be used to set a tag, which can then be used with TagRule().

This PR also adds the missing LuaAction() and LuaResponseAction() that are especially needed since we deprecated addLuaAction() and addLuaResponseAction() in 1.2.0. It also fixes an issue that prevented access to the dnsheader from Lua in responses, for a reason I don't quite understand at the moment.

Checklist

I have:

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