Set the default dashboard for Self Monitoring Project

What does this MR do?

Resolves #121719 (closed). This MR makes it so that when the Self Monitoring project is activated and connected to Prometheus, the default dashboard is self_monitoring_default.yml instead of common_metrics.yml. Note that dashboard itself is implemented in !23851 (merged) and was just copied here temporarily until that MR is merged.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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

Closes #121719 (closed)