Create self-monitoring project in background migration

What does this MR do?

The self-monitoring project was originally created in a post-migration (merged in 12.3, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15071). However, this caused problems like https://gitlab.com/charts/gitlab/issues/1565 since the migration calls application code.

As discussed in https://gitlab.com/gitlab-org/gitlab-ce/issues/66685#note_212886401, this MR changes to use a background migration to create the self-monitoring project.

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/56883

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team