Storybook: Adds story for inserter-draggable-blocks.

[vipul0425]

What?

This PR adds story for InserterDraggableBlocks component.

Why?

Part of: #67165

Testing Instructions

1. Start Storybook by running npm run storybook:dev
2. Open Storybook at http://localhost:50240/
3. Test the story for InserterDraggableBlocks

Screenshots or screencast

Screen.Recording.2024-12-26.at.1.03.57.PM.mov

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Co-authored-by: vipul0425 <[email protected]>

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[t-hamano]

Thanks for the PR!

Unfortunately, this component is an internal component and we decided not to add it to Storybook for internal components (See this comment).

I will close this PR but thank you for your contribution.