Implement edit links

What does this MR do and why?

Adds "view page source" and "edit in webIDE" links to each page.

For reference, here's the Nanoc version: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/lib/helpers/edit_on_gitlab.rb.

Closes #22 (closed)

Screenshots, screen recordings, or links to review app

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Check out this branch
2. Run the site: make view
3. Verify both edit links work for a few pages from each product. Examples:

GitLab

• http://localhost:1313/user/profile/achievements
• http://localhost:1313/administration/operations/moving_repositories/

Charts

• http://localhost:1313/charts/charts/globals/
• http://localhost:1313/charts/backup-restore/backup/

Runner

• http://localhost:1313/runner/development/add-windows-version/
• http://localhost:1313/runner/configuration/feature-flags/

Omnibus

• http://localhost:1313/omnibus/settings/configuration/
• http://localhost:1313/omnibus/settings/database/

Operator

• http://localhost:1313/operator/security_context_constraints/
• http://localhost:1313/operator/backup_and_restore/

Note: Links to _index.md files will not work yet, as we have yet to rename the actual source files (#55 (closed)). Links will point to _index.md, which will eventually be correct.

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.