Enable contextual view (drawer) for GitLab team members

Dogfooding release plan

Make the contextual view available:

1. For GitLab team members only
2. On gitlab-org and gitlab-com
3. Launched from:
   1. Epics listing page - tbd pending the release of the new epics listing page
   2. Epic board
   3. Issue detail page (child widget only)
   4. Objectives detail page (child widget only)