Move remote demo user-images.githubusercontent.com to this repo

[chalin]

• Contributes to Move user-images.githubusercontent.com into this repo #2373
• Contributes to external link checking cleanup - CI: check external links #1052
• Adds demo user-images.githubusercontent.com PNGs to a local folder next to the markdown page that uses the image
• Compresses the images
• Dropped the image URLs from the link checker refcache.
• Copyedits (very minor)

Preview:

• https://deploy-preview-2428--opentelemetry.netlify.app/blog/2022/announcing-opentelemetry-demo-release/
• https://deploy-preview-2428--opentelemetry.netlify.app/docs/demo/scenarios/recommendation-cache/
• https://deploy-preview-2428--opentelemetry.netlify.app/docs/demo/screenshots/

Compressed images with pngquant:

pngquant --ext=.png --force content/en/blog/2022/announcing-opentelemetry-demo-release/sytem-architecture.png
pngquant --ext=.png --force content/en/docs/demo/scenarios/recommendation-cache/grafana-dashboard.png
pngquant --ext=.png --force content/en/docs/demo/scenarios/recommendation-cache/jaeger-waterfall.png
pngquant --ext=.png --force content/en/docs/demo/scenarios/recommendation-cache/jaeger.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/feature-flag-ui.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/frontend-1.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/frontend-2.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/grafana-prometheus.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/gragana-jaeger.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/jaeger-system-architecture.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/jaeger-trace-view.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/jaeger-ui.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/load-generator-ui.png
pngquant --ext=.png --force content/en/docs/demo/screenshots/prometheus.png

[svrnm]

lgtm