Service to create self monitoring project

What does this MR do?

This MR creates a service that can be called to create the self-monitoring project. We will have to call this service in a migration (in a separate MR) since we need to create the self-monitoring project without user interaction.

Later, we might need to add a button to the UI which will call this service to regenerate the project.

The service needs to perform the following:

1. Create a project.
2. Add all admins as project maintainers.
3. Connect the project to the internal Prometheus which is installed by Omnibus.

In order to connect to the internal Prometheus, we need to know the listen address. Therefore this MR also adds an entry to the gitlab.yml.example file for the prometheus listen address. There is a corresponding Omnibus MR to populate the gitlab.yml entry.

This MR also adds a Stepable concern to make the execution of steps in the service clear and concise.

CE MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30153

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/64688

Omnibus MR: omnibus-gitlab!3383 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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