In https://jira.camunda.com/browse/OPT-4054, we add a new sorter pattern for Optimize endpoints that support sorting before returning (not in ES). Event counts does something similar, so we should migrate to the logic to use the new pattern introduced in the linked ticket. We should also consider making it more generic as per https://github.com/camunda/camunda-optimize/pull/2439#discussion_r464505897

ATs:

• Event counts use the new Sorting logic introduced in https://jira.camunda.com/browse/OPT-4054