Merge branch '8.x-3.x' of github.com:contentacms/contenta_jsonapi int…

…o 8.x-3.x

feat: use core media library & new backend theme (#367)

* feat: make it compatible with 8.7

* fix: use the new filesystem services

* feat: update to use the new media library

* feat: use adminimal for the back-end

* feat: use custom favicons

* feat: 8.7 is now stable

feat: add new tutorial for Lando

feat: add new tutorial with Gatsby

Closes #310.

fix: use MySQL to install the site for the tests (#349)

feat: upgrade JSON:API and JSON:API Extras to latest versions

Update JSON:API to ^2.0 and JSON:API Extras to ^3.1 (#343)

Contenta currently requires JSON:API 2.0 at RC. It's now stable. Contenta currently requires JSON:API Extras 3.0. But 3.1 is necessary as of JSON:API 2.0-RC3. So let's bump the minimum to 3.1. (Current stable is 3.2.)

feat: upgrade JSON:API Extras

test: change testing strategy (#339)

fix: pretty print the JSON in the node view