docs: relocate Consul capacity planning page from waf/ to docs/

[krastin]

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

[boruszak]

Good work converting this page using our content templates as a guide.

Please implement the suggested changes and then read through the page again. Then I'll review again for final approval.

[cjobermaier]

Approve once @boruszak suggestions are added.

[boruszak]

Really excellent work.

I left suggestions to correct typos and other style issues. The only thing that's not a suggestion to accept is my comment about using code font and linking out for the lists of metrics.

Approving so you're not blocked.