docs: make external-dns optional in echoserver walkthrough

[prasadkatti]

Description

This PR updates the echoserver walkthrough.

• makes it clear that use of external-dns is completely optional.
• adds a verification section that uses the load balancer DNS name in case external-dns is not used
• removes the spec.rules[0].host in the default manifest. With this in, the example does not work if external-dns is not used. The listener rule does not match because the Host Header does not match the ALB DNS name.
• removes instructions to deploy external-dns and instead links to the right page

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 🌟

[k8s-ci-robot]

Hi @prasadkatti. Thanks for your PR.

I'm waiting for a kubernetes-sigs 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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[codecov-commenter]

Codecov Report

Base: 54.09% // Head: 54.09% // No change to project coverage 👍

Coverage data is based on head (c1d093e) compared to base (9c3f5a2).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2950   +/-   ##
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  Coverage   54.09%   54.09%           
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  Files         144      144           
  Lines        8291     8291           
=======================================
  Hits         4485     4485           
  Misses       3479     3479           
  Partials      327      327           

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[johngmyers]

The indentation is off here. Could you fix it?

[prasadkatti]

It was actually off before. I fixed it here. Reference - https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.26/#ingressrule-v1-networking-k8s-io. The keys host and http need to be at the same indent level.

[johngmyers]

/ok-to-test

[johngmyers]

/lgtm
/assign @M00nF1sh

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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