Use the Qt installer in Docker now that it requires a login

[AdrianChaves]

Now that logging in is an installation requirement, the Dockerfile of Splash, a Qt-based open source JavaScript rendering service used for web scraping, can no longer be built into Docker images.

One workaround seems to be to run the installer without internet connection. That works if you split the Qt installer execution out into a separate Dockerfile, run docker build --network none to build that image. But that only works if you are building Docker images manually, not if you are using hub.docker.com to build them.

Is it possible to have the installer use credentials in an automated way? https://doc.qt.io/qtinstallerframework/noninteractive.html does not seem updated to reflect such an option. Moreover, we would need to be able to have the installer read the credentials from environment variables.

Do you know of any other option, other than building Qt from source, which would significantly slow down image creation, possibly beyond time limits imposed by hub.docker.com?