Translated HelloHTML on WTFAcademy frontend

[Mosamorphing]

This is the first PR of many to make the English version of WTFA courses available to all. It ticks the checklist from the Docusaurus documentation.

1. the docusaurus.config.js has been updated with the en locale
2. the translated English version of HelloHTML has been put in the appropriate folder (i18n/en...)

With this merge, the HelloHTML should be available on the frontend in English language.

[vercel]

@Mosamorphing is attempting to deploy a commit to the WTF Team on Vercel.

A member of the Team first needs to authorize it.