Issues Analytics: loading states updates

Problem

Currently when loading the Issue analytics page, two loading spinners are displayed. One for the chart and another for the table below. Although this behavior doesn't pose and usability risks it may appear that the UI is broken at first glance.

See related discussion: !129656 (comment 1519229839)

Current loading states

Proposal

• Use a spinner for the chart
• Set a min-height on the chart container
• Use a skeleton loader for the table

Current loading states