Blog section for 2025

[chalin]

• Contributes to:
  • [CI] External link checking improvements for 24H2-25H1 #5017
  • Create 2025 blog section and adjust redirects #5873
• Introduces "2025" blog section, including an RSS feed
• Adds link-checker ignore rules for blog sections older than a year
• I'm delaying updating the redirect rules to point to the 2025 section until we have our first 2025 blog post. Otherwise it just looks like the blog section is broken, because no posts are shown.

Preview and redirect tests:

• https://deploy-preview-5874--opentelemetry.netlify.app/blog/ --> redirect to 2025 section still redirects to 2024
• https://deploy-preview-5874--opentelemetry.netlify.app/blog/index.xml --> redirect to 2025 RSS feed still redirects to 2024 RSS feed

[cartermp]

Ah, did not see this was a draft

[chalin]

@cartermp - this is ready for review

IMPORTANT note: this PR introduces link-checker ignore rules for blog posts from 2023 and earlier. That is, we won't be checking any links (external or internal) for those posts. I'd prefer only excluding external link-checking, but it isn't worth the extra setup and computation time to check internal links for all pages (at least not for PR builds). We can always adjust this later if it becomes an issue.