Remove "Edit dashboard" button from self monitoring dashboard

What does this MR do?

On the metrics dashboard UI, there is an "Edit Dashboard" button which, when clicked, takes users to the dashboard's yaml file so that it can be edited.

However, out-of-the-box dashboards like config/prometheus/common_metrics.yml cannot be edited by the user. In order to prevent the "Edit dashboard" button from appearing for out-of-the-box dashboards, a can_edit key is sent to the frontend. Currently, only the config/prometheus/common_metrics.yml dashboard has can_edit set to false. However, the self monitoring dashboard should also not be editable.

This MR:

1. Creates a new out_of_the_box_dashboard key so that out-of-the-box dashboards are easily identifiable.
2. Sets out_of_the_box_dashboard to true for the system dashboard (config/prometheus/common_metrics.yml) and the self monitoring dashboard (config/prometheus/self_monitoring_default.yml).

Issue: #212873 (closed)

Screenshots

Before	After

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