Major revision of SSH signing page for style

What does this MR do?

Because the work in Add verified badge for SSH signed commits (!97248 - merged) is complex and ongoing, I'm moving my docs revisions to this merge request. It targets bwill/ssh-commit-verified-badge instead of master.

For TW leadership, should you stumble onto this merge request: note that this MR is NOT original work. It's my edit to the docs proposed in !97248 (merged). That merge request is at 105 comments and still rising. I'm providing my edits in a separate branch so I don't collide with @bwill's ongoing work.

It overhauls the first draft provided in the companion merge request in the first commit. The second commit adds crosslinks to/from a couple of related pages. I've done it this way to minimize the potential pain of merge conflicts. (Our docs change constantly.)

Related issues

• Related to Add verified badge for SSH signed commits (!97248 - merged) which is where this work will merge into
• Related to Sign commits with your SSH key (#343879 - closed)
• Related to Add revocation for SSH keys (#382984 - closed) which will be the engineering followup.
• Related to SSH key management enhancements to support SSH ... (#375258 - closed) which is another followup.
• Related to Documentation for adding a signing SSH key (#383077 - closed) which requests this work, and some others

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.