Add documentation for the text prop on the Button component

[dhruvkb]

Description

This PR adds documentation for the text prop on the Button component.

Fixes #30621

How has this been tested?

Verified behaviour using the Storybook.

Screenshots

Types of changes

This PR adds missing documentation. Could be classified as a bug fix.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[github-actions]

👋 Thanks for your first Pull Request and for helping build the future of Gutenberg and WordPress, @dhruvkb! In case you missed it, we'd love to have you join us in our Slack community, where we hold regularly weekly meetings open to anyone to coordinate with each other.

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[talldan]

Thanks @dhruvkb. Congrats on your first contribution!