fix: host readiness probe on ipv6 in addition to ipv4 (#3765)

[sjberman]

Cherrypick of #3765

Problem: the readiness probe endpoint is not available on IPv6. This is a problem on IPv6 only clusters when using IPv6 for the pod network. The gateway pod refuses to come up because the readyz condition never fulfills.
Example:

Warning Unhealthy 88s (x160 over 26m) kubelet Readiness probe failed: Get "http://[fdd3:7046:2ad5:430a:39bb:bc6d:e254:a621]:8081/readyz": dial tcp [fdd3:7046:2ad5:430a:39bb:bc6d:e254:a621]:8081: connect: connection refused 

Solution: host the readyz endpoint on IPv6 as well.

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

Fix an issue regarding the readiness probe for the gateway pod on clusters with IPv6 pod networking 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.96%. Comparing base (b504a0e) to head (f4767de).
⚠️ Report is 1 commits behind head on release-2.1.

Additional details and impacted files

@@ Coverage Diff @@ ## release-2.1 #3767 +/- ## =============================================== + Coverage 86.94% 86.96% +0.01%  =============================================== Files 128 128 Lines 16000 16001 +1 Branches 62 62 =============================================== + Hits 13911 13915 +4  + Misses 1922 1919 -3  Partials 167 167 

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.