Create self-monitoring project within a group

What does this MR do?

Currently, all admins are directly added as maintainers of the self-monitoring project (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14511#note_192538664).

This MR will change it to:

1. Create a new group (at the same time as the new project) called Instance Administrators
2. Create the self-monitoring project in that group so that all users who are members of that group have permissions of Owner/Maintainer in the new project.
3. If the project has already been created, do not create it again. It detects if the project has already been created by checking for the project ID in application_settings.

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

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