fix: disabling bot crawling on staging and refactor sitemap to add dates and images

[fpasquet]

[github-actions[bot]]

⚡️🏠 Lighthouse report

Here's the summary:

Path	Performance	Accessibility	Best practices	SEO	PWA
/fix/robots-txt-and-sitemap/	🟢 90	🟢 90	🟢 100	🟢 92	🟠 70
/fix/robots-txt-and-sitemap/fr/authors/ajacquemin/	🟠 73	🟢 90	🟢 100	🟠 85	🟠 70
/fix/robots-txt-and-sitemap/fr/comment-construire-site-web-avec-nextjs/	🟠 78	🟠 80	🟢 100	🟢 92	🟠 70
/fix/robots-txt-and-sitemap/fr/nestjs-le-cycle-de-vie-dune-requete/	🟠 72	🟠 80	🟢 100	🟠 89	🟠 70

Here's the audits:

Path	FCP 1800 <=	LCP 2500 <=	Speed Index 3400 <=	TTI 3800 <=	TBT 200 <=	CLS 0.1 <=
/fix/robots-txt-and-sitemap/	🔴 2437	🟢 2437	🟢 2437	🔴 4336	🟢 6	🔴 0.12
/fix/robots-txt-and-sitemap/fr/authors/ajacquemin/	🔴 2438	🟢 2440	🟢 2832	🔴 4261	🟢 6	🟢 0.01
/fix/robots-txt-and-sitemap/fr/comment-construire-site-web-avec-nextjs/	🔴 2441	🔴 3558	🟢 2441	🔴 4520	🟢 6	🟢 0.03
/fix/robots-txt-and-sitemap/fr/nestjs-le-cycle-de-vie-dune-requete/	🔴 2020	🟢 2020	🟢 2447	🔴 4285	🟢 7	🟢 0.04