Aggreagated Metrics add YAML anchors and aliases

What does this MR do?

At !53553 (merged) was spotted that while providing aggregated metrics definitions repetitive parts may appear especially in terms of list of events included in family of aggregates. In order to DRY up aggregates definitions we can utilize YAML anchor and aliases https://sites.google.com/site/mxu2015kb/computers/computer-languages/yaml/merge-key-language-independent-type feature

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