Skeleton loading for issue board

Resources

FE @jschatz1

Description

We currently show a spinner while we load issues in the issue board. In the Add issues modal we currently don't have any loading indicators (to be solved with gitlab-ce#29615)

I propose we use skeleton loading, which consist in showing a simplified version of the content that will be loaded. It would look somethig like this in the Add issue modal

In this animation every field lights up at the same time. I think it would look a little better if there was a "swipe" effect, where they light up from left to right, but my prototyping skills are not there yet 😅

Problem

Currently, the issue count per list is shown as "0" when the page first loads, and then it changes to the real number when the issues are loaded. This should be fixed so that users are not given false information.

Design

• See skeleton loading requirements and example here: gitlab-design#35 (closed)
• Check out this comment for dev implementation tips: gitlab-design#35 (comment 36802914)