Milestone page with burndown chart, issues, merge requests, and filtering on labels

As part of https://gitlab.com/gitlab-org/gitlab-ee/issues/3043, the FE team would like to request a burndown chart view for labels.

Example

Benefits

• Enable each functional team to easily track their teams progress on each release (during the release)
• Could also be used to track regression during a milestone

Problem to be solved

• View a burndown chart relevant to labels I care about.
• View the issues / merge requests I care about, filtered by the labels.
• The labels section may need to be redesigned to reflect this new UI functionality.
• Make sure participants still make sense.