Wildcard: Tabs - add scrolling fade-out gradients

Created by: oleggromov

As pointed out in the previous PR, it would be great to have not only scrolling but also a visual hint of the fact that it's scrollable.

This PR adds gradients as suggested

https://user-images.githubusercontent.com/2196347/169811100-82f55c72-3062-4dba-82a9-698ae7634b1c.mov

Test plan

1. Pull the branch
2. Run wildcard storybook: yarn storybook:wildcard
3. Check the component in light and dark themes

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.