Hooks: Document 'hookName' and 'namespace' parameters

[Mamaduka]

What?

Closes #40840.

PR adds documentation for 'hookName' and 'namespace' parameters. Based on #40840.

Testing Instructions

None.

[github-actions]

Flaky tests detected in a6ca96f.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/17118159357
📝 Reported issues:

• [Flaky Test] ensures List View global shortcut works properly #51533 in /test/e2e/specs/editor/various/list-view.spec.js
• [Flaky Test] should refresh the page when stylesheet loading fails #71135 in /test/e2e/specs/interactivity/router-styles.spec.ts

[github-actions]

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[Copilot]

Pull Request Overview

This PR adds documentation for the 'hookName' and 'namespace' parameters to the hooks package README, addressing issue #40840 by providing clear parameter specifications and validation rules.

• Added a new "Parameters" section documenting hookName and namespace parameter requirements
• Specified validation rules for both parameters including character restrictions and formatting requirements

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