Show actual date on Merge Request or Commit, rather than rounded down approximation

When reviewing an older merge request, it is difficult to figure out when it was actually merged. Instead of saying '1 year ago', we should show the date in ISO format: https://about.gitlab.com/handbook/communication/#communicating-dates-and-time

For example, this MR says merged 1 year ago, but it was really almost 2 years ago (the commit was on 2021-03-12). gitlab-com/www-gitlab-com!77263 (merged)

Even when viewing the actual Commit, it also shows 'authored 1 year ago' gitlab-com/www-gitlab-com@f4f09649