Add ShimmerEffect component

[lappemic]

Got into flow 😄

Added a new ShimmerEffect component.

What's new:

• Created shimmer-effect.tsx with the ShimmerEffect component
• Updated animation-preview.tsx to show ShimmerEffect examples
• Added documentation for ShimmerEffect in shimmer-effect.content.ts
• Updated side navigation to include ShimmerEffect
• Updated docs content configuration to include ShimmerEffect

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