Add trend indicators to the Exec dashboard comparative table

What does this MR do and why?

Issue: #378316 (closed)

Adds metric trend indicators to the analytics Exec dashboard. In order to determine the trend for two months prior, we need to send an additional request which doesn't appear in the output table.

Screenshots or screen recordings

Before After
Screen_Shot_2022-11-08_at_2.02.39_PM Screen_Shot_2022-11-08_at_2.01.55_PM

How to set up and validate locally

  1. Enable the Exec dashboard
    Feature.enable(:group_analytics_dashboards_page)
  2. Visit the exec dashboard: http://gdk.test:3000/groups/${YOUR_GROUP}/-/analytics/dashboards

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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