chore(GlChart): migrate stories to CSF

What does this MR do?

This migrates GlChart stories to the Component Story Format.

Here's the relevant page in the review app: http://1270-migrate-chart-stories.64.227.120.153.nip.io/?path=/docs/charts-chart--default

Note: Controls have been disabled globally on the stories as we currently don't expose any knobs. Due to some Storybook-related issue, controls still appear in the docs page, even though they don't have any effect. This should be fixed in Storybook 6.2.

Closes #1270 (closed)