Minor cleanup to rest api page

[kprosise]

Focus was on changing the api link so that customers not logged in would see a notice of such rather than a page error. An admonition to this effect was added.
All links to the api were changed as otherwise they would need individual references.

Other minor clean done.

No related ticket, quick fix.

PR Template and Checklist

Please complete as much as possible to speed up the reviewing process.

Readiness and adding reviewers as appropriate is required.

All PRs should be reviewed by a technical writer/documentation team and a peer.
If effecting customers—which is a majority of content changes—a member of Customer Success must also review.

Readiness

• Merge (pending reviews)
• Merge after date or event
• Draft

Overview

Follows up to discussion of issue.

Checklist

• Run spelling and grammar check, preferably with linter.
• Avoid changing any header associated with a link/reference.
• Review for wordiness
• Match tone and style of page/section.
• Run make linkcheck.
• View HTML in a browser to check rendering.
• Use semantic newlines.
• follow best practices for commits.
  • Descriptive title written in the imperative.
  • Include brief overview of QA steps taken.
  • Mention any related issues numbers.
  • End message with sign off/DCO line (-s, --signoff).
  • Sign commit with your gpg key (-S, --gpg-sign).
  • Squash commits if needed.
• Request PR review by a technical writer and at least one peer.

[doanac]

Docs for 1e6b5ce are browsable at: https://ci.foundries.io/projects/fio-docs/builds/2787/docs/artifacts/html/index.html