Provide a correct empty state of charts

Description

Our charts do not provide a reasonable empty state when they contain no data. For example, in the case of he line chart we show an empty canvas with an empty tooltip which looks buggy:

gitlab-org/gitlab!182241 (comment 2376675994)

Even though our charts have required: true data prop, the data can easily be an empty array, leading to this empty screen easily.

Proposed solution

Allow our charts to display an intentionally empty canvas which is tested by storyshots and allow a default empty value in the data.