chore: add migration script to add CreatedAt property to Vault CONF# items

[craigzour]

Summary | Résumé

Part 2 of https://github.com/cds-snc/platform-forms-client/issues/4287

• Create migration script to add CreatedAt property to existing Vault CONF# items. The value assigned to that property is taken from the original associated NAME# item.

[github-actions[bot]]

:test_tube: Review environment

https://ax3md33orvid3uhlbdtvfmm4we0kvjle.lambda-url.ca-central-1.on.aws/