Backport of Propose new changes to APIgw upgrade instructions into release/1.16.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #17693 to be assessed for backporting due to the inclusion of the label backport/1.16.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
will see the cherry-picked commits up to, not including, the commit where
the merge conflict occurred.

The person who merged in the original PR is:
@im2nguyen
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: POST https://api.github.com/repos/hashicorp/consul/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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Description

Testing & Reproduction steps

Links

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• a31c3b3 - 40e2659 - 0794c0d - d3d9f4f - 3de6156 - bf70fa9 - 2ef136b - b7f65ce

[hashicorp-cla]

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1 out of 2 committers have signed the CLA.

• im2nguyen
• temp

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[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR

[david-yu]

@im2nguyen this looks like a failed backport