Update backups page to mention our self-managed backups

[ebenezerdon]

What does this PR do?

Updates the backups page in the docs to mention our self-managed backups.

Test Plan

• Run the app and navigate to /docs/advanced/security/backups
• Confirm that the content and link reference are displayed correctly

[ebenezerdon]

@stnguyen90 I've pushed a new commit with revision