Upgrade to Hugo 0.125.4 + temp template

[chalin]

• Enable light/dark mode menu #4346 had too many moving parts, so I'm factoring out the Hugo update into this PR
• Updating only Hugo requires a workaround:
  • This PR introduces the temporary empty template layouts/_internal/google_analytics_async.html
• This version of Hugo includes a fix of:
  Twitter og:description doubly escaped by Hugo 0.125.x gohugoio/hugo#12418

---

$ (cd public && git diff -bw --ignore-blank-lines -I '<meta |^\s$|"\s*\/>$|">$|&rsquo;|&amp;') | grep ^diff | grep -v '\.xml$' | head -30
diff --git a/blog/2023/euwg-future-of-observability-panel/index.html b/blog/2023/euwg-future-of-observability-panel/index.html
diff --git a/blog/2023/humans-of-otel/index.html b/blog/2023/humans-of-otel/index.html
diff --git a/community/index.html b/community/index.html
...

---

For later, descriptions whose renderings should be double checked under Hugo 0.125.x:

• https://opentelemetry.io/community/end-user/otel-in-practice/
  https://deploy-preview-4346--opentelemetry.netlify.app/community/end-user/otel-in-practice/
• https://opentelemetry.io/docs/languages/go/
  https://deploy-preview-4346--opentelemetry.netlify.app/docs/languages/go/