Use consistent check for if dashboard is embedded

What does this MR do?

!26329 (merged) swapped all dashboard services to a new check for whether the dashboard will be embedded! The ClusterMetricsEmbedService was in MR at the time though, and it was decided to hold off on the update until after it was merged.

This updates the ClusterMetricsEmbedService to use the same method as all the other services in app/services/metrics/dashboard

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [n/a] Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [n/a] Database guides
• [n/a] 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.
• [n/a] Tested in all supported browsers
• [n/a] Informed Infrastructure department of a default or new setting change, if applicable per definition of done