Add support for alt text of logo for navbar & footer in translations builds

[Mysterious-Dev]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.

Motivation

This PR can allow more control for translations by the addition of footer & navbar alt text for logo.

It's a detail but that can be usefull to translate the alt text for footer Logo of docusaurus website (https://github.com/facebook/docusaurus/blob/main/website/docusaurus.config.js#L622) to be more consistent.

Test Plan

Translations tests have been updated for the package docusaurus-theme-classic ^^.

Test links

Deploy preview: https://deploy-preview-8551--docusaurus-2.netlify.app/

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 65	🟢 97	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 80	🟢 100	🟢 100	🟢 100	🟢 90	Report

[slorber]

curious to know why you decided to close it? 🤔