Gotenberg v7 does not use environment variables anymore, but command's flags. See: https://gotenberg.dev/docs/get-started/docker-compose#modules-properties
This commit adapts to the latest breaking changes from Gotenberg 7. It also freezes the usage of the Gotenberg server to v7.x. Doing this prevents further breaking changes leaking in our code base. * refs #1250
* refs https://github.com/sphinx-doc/sphinx/issues/4098
Uli