dnsdist: Filter on opcode, records count/type, trailing data

dnsdist: Filter on opcode, records count/type, trailing data

* Add `OpcodeRule()` to filter on opcode + DNSOpcode.* Lua values
* Add `TrailingDataRule()` to filter queries with trailing data
* Add `RecordsCountRule(section, minCount, maxCount)` to match on
the number of records in a given section
* Add `RecordsTypeCountRule(section, type, minCount, maxCount)` to
match on the number of records of type `type` in a given section
* Add DNSSection.* Lua values
* Add DNSClass.* Lua values