fix(parser) bound v6 targets properly

[rainest]

What this PR does / why we need it:

Surround IPv6 Endpoint addresses with brackets when generating a target. Without these, the target port suffix parses as part of the address and assigns an incorrect address and (default) port.

Which issue this PR fixes:

Fixes #4369. Thanks @pnathan for locating the problem section of the parser code for us!

Special notes for your reviewer:

CI doesn't do v6-only at present. We should maybe consider that as a nightly test. There are quite possibly other v6-only problems. We don't have the scaffolding to actually do that yet though, so spot testing it is!

Local testing using https://kind.sigs.k8s.io/docs/user/configuration/#ip-family was to confirm via the stock image:

$ curl -ksv "https://[fc00:f853:ccd:e793::50]:8444/upstreams/httpbin.default.80.svc/targets"  | jq

{
  "data": [
    {
      "weight": 100,
      "tags": null,
      "id": "97177439-6e38-5366-9aae-415d0fed84fe",
      "target": "[fd00:0010:0244:0000:0000:0000:000e:0080]:8000",
      "created_at": 1689977170.046,
      "updated_at": 1689977170.046,
      "upstream": {
        "id": "5e5b8bb7-173e-5982-bbe4-56faf6a09264"
      }
    }
  ],
  "next": null
}

$ kubectl get endpointslices.discovery.k8s.io 
NAME            ADDRESSTYPE   PORTS   ENDPOINTS               AGE
httpbin-6jsgl   IPv6          80      fd00:10:244::e          12m
kubernetes      IPv6          6443    fc00:f853:ccd:e793::2   41m

After putting an image with this change in place, no more errant 80 octet, or whatever you call v6 segments:

$ curl -ksv "https://[fc00:f853:ccd:e793::50]:8444/upstreams/httpbin.default.80.svc/targets"  | jq
{
  "data": [
    {
      "updated_at": 1689978524.721,
      "id": "d347916d-a502-5b01-94bf-1be634433a7e",
      "weight": 100,
      "upstream": {
        "id": "5e5b8bb7-173e-5982-bbe4-56faf6a09264"
      },
      "target": "[fd00:0010:0244:0000:0000:0000:0000:000e]:80",
      "created_at": 1689978524.721,
      "tags": null
    }
  ],
  "next": null
}

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Patch coverage: 100.0% and project coverage change: -0.3% ⚠️

Comparison is base (3339b60) 66.5% compared to head (5cb4065) 66.3%.

❗ Current head 5cb4065 differs from pull request most recent head fb2afa9. Consider uploading reports for the commit fb2afa9 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4391     +/-   ##
=======================================
- Coverage   66.5%   66.3%   -0.3%     
=======================================
  Files        158     158             
  Lines      18556   18555      -1     
=======================================
- Hits       12347   12302     -45     
- Misses      5456    5510     +54     
+ Partials     753     743     -10     

Files Changed	Coverage Δ
internal/dataplane/parser/parser.go	79.1% <100.0%> (+0.2%)	⬆️

... and 11 files with indirect coverage changes

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[randmonkey]

Generally good, but can we add some unit tests for the fix?