Improve label selection

Problem

• The usability of labels is not that great
• Users don't have an overview of which labels are selected while creating a new issue

Solution

Let's iterate on solutions how we can improve adding labels.

A first draft I've made:

Current	Select solution	New component

Implementation

• Component created - Created a new Vue label selector for issuable f... (gitlab-org/gitlab!90222 - merged)
• Added to issues and MRs - Add improved label selection to issues and MRs ... (gitlab-org/gitlab!88908 - merged)
• Added to epics
• Added to test cases