Enh/improve skeletton loading (#810)

* Update skeleton styling

* Update skeleton color

* Remove useless color

* Add loading test case

* naming

* Improve test

* Fix colors

* Add import

* Lint

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Co-authored-by: Charles Bochet <charlesBochet@users.noreply.github.com>

front/.storybook/preview.ts

@@ -4,6 +4,7 @@ import { ThemeProvider } from '@emotion/react';
 import { withThemeFromJSXProvider } from '@storybook/addon-styling';
 import { lightTheme, darkTheme } from '../src/modules/ui/themes/themes';
 import { RootDecorator } from '../src/testing/decorators';
+import 'react-loading-skeleton/dist/skeleton.css';
 import { mockedUserJWT } from '../src/testing/mock-data/jwt';
 initialize();