Total time spend in milestone

Description

A total count of time spend in the milestone.

Proposal

Display it in the right menu when on the milestone page.

Note that the units of the total time spent should be using the same automatic format as when you are entering / displaying time spent in the comment box of an issue, i.e. https://docs.gitlab.com/ce/workflow/time_tracking.html

Links / references

Documentation blurb

Overview

We need it to invoice clients based on the number of hours.

Use cases

Project management

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml