Backport of [release/1.15.3] Add cloud stanza documentation into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #17311 to be assessed for backporting due to the inclusion of the label backport/1.15.

🚨

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:
@hanshasselberg
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: "53b0ee929b05888cbb073a7cefb64b3fc7f38a56", automatic backport requires rebase workflow

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

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Description

This PR adds documentation for the HCP cloud stanza.

PR Checklist

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

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Overview of commits

• 39e273a - f563ed0 - 53b0ee9

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

Auto approved Consul Bot automated PR