feat(blog): enhance blog functionality and SEO

- Added a new '/blog' route to middleware for improved navigation.
- Updated sitemap to dynamically include blog posts and series URLs.
- Enhanced blog page metadata with Open Graph and Twitter card information.
- Implemented structured data for blog posts and series to improve SEO.
- Removed outdated blog post "Week 1: De Kickoff" from content.
- Introduced optional OG image field in blog frontmatter for better sharing visuals.

middleware.ts

@@ -50,6 +50,7 @@ export async function middleware(request: NextRequest) {
     '/update-password',
     '/auth/callback',
     '/contact',
+    '/blog',
     '/documentatie',
     '/api/leads',
     '/robots.txt',