[APM] Breakdown Top dependencies API

[cauemarcondes]

Currently the GET /internal/apm/dependencies/top_dependencies fetches all values with timeseries data and the comparison values. This slows down the response of this API.

The goal is to split this API to fetch the dependency names and the metric values (to sort the items correctly), then on a follow up request query the timeseries statistics and its comparison values.

[elasticmachine]

Pinging @elastic/obs-ux-infra_services-team (Team:obs-ux-infra_services)