Move core plugins docs to documentation website

[NataliaTepluhina]

This PR is designed to move core plugins docs to CLI documentation website. This will allow us to keep documentation up-to-date with the latest release.

Plugins to move:

• Babel
• TypeScript
• ESLint
• PWA
• Jest
• Mocha
• Cypress
• Nightwatch

Close #4117

[NataliaTepluhina]

@Akryum @sodatea @LinusBorg could you please take a look at this one?

Important note: these docs are relevant for 3.8.2 version, i.e. the latest changes to PWA doc from 4.0.0-alpha are not included. The reason is described here

[sodatea]

Thanks for the help!
I like the idea of moving the docs to the website, it's easier for translation collaboration.

Though, as for the links on the website, I've already redirected them to v3 branch 821067f (The deployed version lies in the docs branch)

As for the developing v4 docs, instead of manually copying-and-pasting from the README files, what about writing a script to automatically generate the docs page on publishing new versions? So that it won't be out of sync.

[NataliaTepluhina]

Ready 😅