update external dns manifest and docs

[kishorj]

Issue

External DNS example is out of date.

Description

Update external-dns sample manifest and docs.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[M00nF1sh]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kishorj, M00nF1sh

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• OWNERS [M00nF1sh,kishorj]

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[shyamjvs]

Nice! Thanks for making this doc change @kishorj

/lgtm

[k8s-ci-robot]

@shyamjvs: changing LGTM is restricted to collaborators

In response to this:

Nice! Thanks for making this doc change @kishorj

/lgtm

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[codecov-commenter]

Codecov Report

Base: 54.05% // Head: 54.05% // No change to project coverage 👍

Coverage data is based on head (2a75dd1) compared to base (7367f60).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2895   +/-   ##
=======================================
  Coverage   54.05%   54.05%           
=======================================
  Files         144      144           
  Lines        8278     8278           
=======================================
  Hits         4475     4475           
  Misses       3479     3479           
  Partials      324      324           

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