Insights: Add drill down from charts - support drill downs for all "Issue" and "Merge request"

Overview

This is a followup to the MVC of Insights: Drill down from charts (#372215 - closed).

Following this customer request, and this Dogfooding feedback.

Proposal

• Add drill downs for all "Issue" and "Merge request" related reports under the Insights.
• Insights for groups - Issue --> group /issues_analytics
• Insights for groups - MRs --> group productivity_analytics
• Insights for projects - Issue --> project /issues_analytics
• Insights for projects - MRs --> project /merge_request_analytics
• Should only inherit labels for now
• Create new event definition for merge request charts for Internal Event Tracking