Related merge requests in issue design - New elements

Follow up of https://gitlab.com/gitlab-org/gitlab-ce/issues/47007 with new UI elements

Also, the tooltip's timezone should be rendered via the browser

See design specs linked in https://gitlab.com/gitlab-org/gitlab-ce/issues/47007

Information to display:

• Status (open/closed/merged)
• Path and ID
• Title (link to the merge request)
• Assignees (link to each user's profile)
  • Multiple assignees: follow the related issues design specs which support multiple assignees
• Milestone (out of scope)
• Items left to allow merge (see the Items, states, and tooltips spec for full details and explanation)
  • To be implemented in https://gitlab.com/gitlab-org/gitlab-ce/issues/60876
• Pipeline status (link to pipeline)