WIP: Blog post for instance integrations

Closes #6949 (closed)

Checklist for writer

• Link to issue added, and set to close when this MR is merged
• Due date and milestone (if applicable) added for the desired publish date
• If time sensitive
  • Added ~"priority" label
  • Mentioned @rebecca to give her a heads up ASAP
• Blog post file formatted correctly, including any accompanying images
• All relevant frontmatter included
• Review app checked for any formatting issues
• Reviewed by fellow team member
• If approval before publishing is required
  • Any required internal or external approval for this blog post has been granted (please leave a comment with details)
• Assign to @rebecca for review

Pending MR

gitlab-org/gitlab!25587 (merged) should be merged when this goes live