Only install the required dependencies for chromium/firefox and nothing more.
We get the rest via playwright.

The behaviour should be the same, except the deployer command
is now independent of the CWD.

We also no longer ship deployer in the docker image, but install
it via composer, so it's easier to update.

It has a new enough firefox now

This way we have a central place for the CI image config and also testing
is faster because not everythign has to be installed on each run.