Backport of update serf links into release/1.20.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #21797 to be assessed for backporting due to the inclusion of the label backport/1.20.

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The person who merged in the original PR is:
@jmurret
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

Related to docs moving from serf.io to the serf repo: hashicorp/serf#743

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Overview of commits

• 024c15e - 148b35c - aaeca94 - 9242b7e

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

Auto approved Consul Bot automated PR