block-attributes: Add role attribute explanation

[im3dabasia]

What?

Closes : #65614
Related comment: #65484 (review)

Add a missing role field, in the block-attributes.md for clarity among block developers

Why?

The role field was stabilised in WordPress 6.7, but was not exposed in the developer documentation, in this https://github.com/WordPress/gutenberg/blob/trunk/docs/reference-guides/block-api/block-attributes.md

How?

Updated the Docs.

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Co-authored-by: fabiankaegy <fabiankaegy@git.wordpress.org>
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[fabiankaegy]

Left one small suggestion :) Other than that this is good to go! Thanks for the addition!

[fabiankaegy]

It might be worth also linking to the dev note Or making sure all the same contents are covered: https://make.wordpress.org/core/2024/10/20/miscellaneous-block-editor-changes-in-wordpress-6-7/#stabilized-role-property-for-block-attributes

[im3dabasia]

It might be worth also linking to the dev note

I have added a link to the dev note the final appearance of the document looks something like this.

Let me know your thoughts if any improvements are needed.

[fabiankaegy]

Ship It :)