Add basic Racket support (#4098)

.github/labeler.yml

docs/AddingALanguage.md

etc/config/racket.amazon.properties

etc/config/racket.defaults.properties

examples/racket/default.rkt

lib/compilers/_all.js

lib/compilers/racket.ts

lib/languages.ts

types/languages.interfaces.ts

views/resources/logos/racket.svg

webpack.config.esm.js