Component groups: Skeleton table

[andrew-ronaldson]

The Skeleton table component will require gradient animations in Figma prototyping. This functionality will only be visible when sharing a prototype link so this is lower priority than other Component groups.

### Tasks
- [x] Add Skeleton table to v6 kit

[kaylachumley]

@andrew-ronaldson Ready for review - Figma Prototype here

[kaylachumley]

Proposed Motion tokens: While the gradient is loading from left to right, use Global--Motion--Timing-Function--Accelerate and Global--Motion--Duration--Short

[andrew-ronaldson]

Closed as completed in Extensions library