Extract Aggregations Class

[JPrevost]

This is a small change to isolate it from a larger change coming soon where we add a lot more aggregations. Moving Aggregations to its own Class with each Aggregation getting it's own Method with no functional changes is the full scope of this PR.

The next PR will make changes to this new class but the changes will be much easier to follow if we land this small part first.

Developer

• All new ENV is documented in README
• All new ENV has been added to Heroku Pipeline, Staging and Prod
• ANDI or Wave has been run in accordance to
  our guide and
  all issues introduced by these changes have been resolved or opened as new
  issues (link to those issues in the Pull Request details above)
• Stakeholder approval has been confirmed (or is not needed)

Code Reviewer

• The commit message is clear and follows our guidelines
  (not just this pull request message)
• There are appropriate tests covering any new functionality
• The documentation has been updated or is unnecessary
• The changes have been verified
• New dependencies are appropriate or there were no changes

Requires database migrations?

NO

Includes new or updated dependencies?

NO

[matt-bernhardt]

This seems straightforward enough; I'm somewhat amused that making this change results in an increase in code coverage (more lines in place means a higher percentage of tested lines of code :-) )

I've checked the playground in the review app and see the same aggregation options, working the same way we expect.