Comments Pagination: Add example attribute to block

[Infinite-Null]

Part of #64707

What?

This PR adds an example attribute to the Comments Pagination block’s block.json to provide a default paginationArrow.

Testing Instructions

1. Open a post or page in the WordPress block editor.
2. Open the block inserter by clicking the “+” button.
3. Add comments block and search for comments pagination block.
4. Hover over the comments pagination block in the inserter.

Screenshots

Before	After

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Co-authored-by: Infinite-Null <[email protected]>

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