Plans Next [Storybook]: Create stories for the PlansFeaturesMain component

[oswian]

wp-calypso/client/my-sites/plans-features-main/index.tsx

This component is responsible for rendering FeaturesGrid, ComparisonGrid etc in a single view.

Stories for PlansFeaturesMain will likely correspond to different variants / user flows, so this task should be broken down rather than tackling all at once. The first story will likely involve most of the effort, with other variants/flows replicating the same setup.