fix: updates labels to include units in metrics

What does this MR do?

• Updates config/prometheus/cluster_metrics.yml so that the y_label and label include units
• Updates config/prometheus/common_metrics.yml so that the y_label and label include units

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #12602 (closed) (2/2)