feat: add multiple addresses support for DNS modifier

[eddc005]

Completes #137 . The DNS modifier now takes a list of addresses. One of the addresses is picked by the hash of the DNS query.

This PR forces a change to the rule.yaml file. Existing rule file will break as following:

2000-01-01T00:00:00+00:00       FATAL   failed to load rules    {"error": "yaml: unmarshal errors:\n  line 22: cannot unmarshal  !!str `1.1.1.1` into []interface {}"}

An example new modifier file

- name: v2ex dns poisoning
  action: modify
  modifier:
    name: dns
    args:
      a:
      - "192.0.2.1"
      - "192.0.2.2"
      - "192.0.2.3"
      - "198.51.100.1"
      - "198.51.100.2"
      aaaa: 
      - "2001:db8::1234:5678"
      - "2001:db8::abcd:ef12"

  expr: dns != nil && dns.qr && any(dns.questions, {.name endsWith "v2ex.com"})

[haruue]

Loading the list from an external file might be better.

And I think it is possible to determine the IP family when parsing, so splitting the options to "a" and "aaaa" would not be necessary.

- name: ...
  action: modify
  modifier:
    name: dns
    args:
      a: "192.0.2.33"
      aaaa: "2001:db8::abc:123"
      file: "./ipslist.txt"
      list:
        - "192.0.2.66"
        - "192.0.2.67"
        - "2001:db8::ccc:ddd"
        - "2001:db8::abcd:1234"
  expr: ...

[eddc005]

Hi @haruue ! I've updated the PR to support exactly this format. Let me know what do you think about this :)

- name: ...
  action: modify
  modifier:
    name: dns
    args:
      a: "192.0.2.33"
      aaaa: "2001:db8::abc:123"
      file: "./ipslist.txt"
      list:
        - "192.0.2.66"
        - "192.0.2.67"
        - "2001:db8::ccc:ddd"
        - "2001:db8::abcd:1234"
  expr: ...

Added a and aaaa back for backward compat.