feat: migrate to Storybook 6

[gmukul01]

Description

Migrate to Storybook 6

Additional context

https://medium.com/storybookjs/storybook-6-0-1e14a2071000
https://medium.com/storybookjs/storybook-6-migration-guide-200346241bb5

[phoenixTW]

I will raise a PR soon for the upgrade