Update changelog, add missing source file

docs/site/changelog/2021-02-09-20.12.0.md

docs/site/changelog/2021-03-27-21.03.0.md

docs/site/changelog/2021-04-28-21.03.1.md

docs/site/changelog/2021-05-10-21.03.2.md

docs/site/changelog/2021-05-18-21.03.3.md

docs/site/changelog/2021-07-07-21.06.0.md

docs/site/docusaurus.config.js

docs/site/src/theme/CodeBlock.tsx