feat: host collector for DNS

[nvanthao]

Description, Motivation and Context

New host collector DNS that will run DNS query to various domains. Will help with DNS issue such as detect wildcard DNS used.

Fixes: https://app.shortcut.com/replicated/story/112277/analyse-search-domains-with-wildcard-dns-records-on-hosts
Demo: https://asciinema.org/a/Ma1i4T0xp50ODNswrfeHTrOTo

Sample spec

kind: SupportBundle
metadata:
  name: sample
spec:
  hostCollectors:
    - dns:
        collectorName: "wildcard-check"
        hostnames:
          - "*"
  analyzers:
    - jsonCompare:
        checkName: Detect wildcard DNS
        fileName: host-collectors/dns/wildcard-check/result.json
        path: "resolvedFromSearch"
        value: |
          ""
        outcomes:
          - fail:
              when: "false"
              message: "Possible wildcard DNS detected at: {{ .resolvedFromSearch }}. Please remove the search domain OR remove the wildcard DNS entry."
          - pass:
              when: "true"
              message: No wildcard DNS detected.

Sample output when there's wildcard DNS configured

{
  "query": {
    "*": [
      {
        "server": "127.0.0.53",
        "search": ".foo.testcluster.net.",
        "name": "*.foo.testcluster.net.",
        "answer": "*.foo.testcluster.net.\t60\tIN\tA\t192.1.2.3",
        "record": "192.1.2.3"
      },
      {
        "server": "127.0.0.53",
        "search": ".c.replicated-qa.internal.",
        "name": "*.c.replicated-qa.internal.",
        "answer": "",
        "record": ""
      },
      {
        "server": "127.0.0.53",
        "search": ".google.internal.",
        "name": "*.google.internal.",
        "answer": "",
        "record": ""
      },
      {
        "server": "127.0.0.53",
        "search": ".",
        "name": "*.",
        "answer": "",
        "record": ""
      }
    ]
  },
  "resolvedFromSearch": ".foo.testcluster.net."
}

Checklist

• New and existing tests pass locally with introduced changes.
• Tests for the changes have been added (for bug fixes / features)
• The commit message(s) are informative and highlight any breaking changes
• Any documentation required has been added/updated. For changes to https://troubleshoot.sh/ create a PR here

Does this PR introduce a breaking change?

• Yes
• No

[diamonwiggins]

Should we have an option on the collector to specify ndots, and then if its set update the DNS config here to set that value?

https://github.com/miekg/dns/blob/master/clientconfig.go#L12-L19

[diamonwiggins]

ndots is a good example, but anywhere someone might want to override the config from the collector could be useful to expose.

[diamonwiggins]

Looking further, since you're iterating and appending every search domain found on the host to see if one of them resolves something we suspect it shouldn't, then the ndots stuff probably isn't needed? So whether you decide to add that or not completely up to you at this stage.