Backport of docs: relocate Consul capacity planning page from waf/ to docs/ into release/1.18.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #21088 to be assessed for backporting due to the inclusion of the label backport/1.18.

🚨

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:
@krastin
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: unable to process merge commit: "530b458b9923858422582d54cd2ec48e7182036e", automatic backport requires rebase workflow

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

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Description

Do not merge until the following related PR is approved and ready for merge:
https://github.com/hashicorp/tutorials/pull/2091

Moving the Consul capacity planning page from WAF/ to docs/ in the shape of an Overview template page.

Testing & Reproduction steps

None

Links

• Consul capacity planning

PR Checklist

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

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Overview of commits

• b9ca305 - cba2bd2 - 530b458 - 3cd2af2 - 0aaabc8 - 6e46b98

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

Auto approved Consul Bot automated PR

[krastin]

Backport looking good