Upgrade dependencies

[ckenst]

Need to upgrade:

1. Ruby to 2.7.4
2. github-pages to latest (228)
3. nokogiri to latest
4. bundler version to latest
5. Jekyll to latest
6. Jekyll container image to match

[ckenst]

Need to split these up and only install dependencies as they make sense. Then match them to the docker versions.

[ckenst]

Blocked by #631