Discontinue use of a single DNS query to validate an endpoint name

[jacksontj]

What this PR does / why we need it:

This resolves issue #4670 by not using a single DNS query to determine the validity of a configured DNS name.

Fixes #4670

Special notes for your reviewer: I have created a test build of this (https://quay.io/repository/jacksontj/ingress-nginx?namespace=jacksontj) and am running it without issue, and can confirm the fix. With this fix it does leave those "broken" services spamming the logs, which is why I have included an addition to the lua log lines to clarify the situation.

[k8s-ci-robot]

Hi @jacksontj. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[ElvinEfendi]

/ok-to-test

[codecov-io]

Codecov Report

Merging #4671 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4671      +/-   ##
==========================================
- Coverage   58.69%   58.66%   -0.03%     
==========================================
  Files          88       88              
  Lines        6762     6762              
==========================================
- Hits         3969     3967       -2     
- Misses       2355     2356       +1     
- Partials      438      439       +1

Impacted Files	Coverage Δ
internal/ingress/controller/endpoints.go	93.75% <100%> (ø)	⬆️
internal/ingress/metric/collectors/process.go	88.29% <0%> (-2.13%)	⬇️

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[jacksontj]

@ElvinEfendi After those test runs I see that a few places test specifically for this behavior, so I have changed the controller to validate the DNS name (the k8s library for this is already a dependency). If you'd prefer to keep that out I can definitely remove it again :)

[jacksontj]

/retest

[jacksontj]

The lua test stuff was giving me some trouble, so I've split that out into another PR -- #4673

[jacksontj]

/assign @ElvinEfendi

[jacksontj]

@ElvinEfendi tests are passing, so this PR should be ready to merge :)

[aledbf]

@jacksontj please don't assign PRs manually. Thanks

[aledbf]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, jacksontj

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