Resolve "Rename cluster_metrics_new.yml"

What does this MR do?

Removes _new suffix from dashboard configuration file name. File was added in !15709 (merged). Since this dashboard is no longer considered to be new, filename should represent that.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry //not required
• Documentation created/updated or follow-up review issue created //not 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.

Closes #14740 (closed)