Recognize other out-of-the-box metrics dashboards

What does this MR do?

Metrics dashboards exist in 2 locations:

1. The projects repository under .gitlab/dashboards.
2. Out of the box dashboards are defined in the Gitlab code under config/prometheus.

In order to shorten dashboard URLs, we apply .gitlab/dashboards as a prefix to any metrics dashboard path other than config/prometheus/common_metrics.yml. This allows us to use dashboard.yml instead of .gitlab/dashboards/dashboard.yml, while still allowing config/prometheus/common_metrics.yml. However, there can be more out of the box dashboards defined under config/prometheus.

This MR changes the logic to not add the prefix for any dashboard under config/prometheus. This allows us to define more out of the box dashboards in config/prometheus.

Issue: #218649 (closed)

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