Displays milestone remaining days only when it's present

Backport from EE https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/944#note_19691183

Thanks @dbalexandre

enabled an automatic merge when the build for ef848c5c succeeds

merged

mentioned in commit e17758c2

@smcgivern I'm guessing ~"Pick into Stable" this one also since its EE counterpart is ~"Pick into Stable"?

@eReGeBe right, added!

added ~149423 label

changed milestone to %8.14

Picked into 8-14-stable. Will go into 8.14.5.

removed ~149423 label

mentioned in issue #25623 (closed)

mentioned in commit cd4fc106