Check Dockerfile does not install useless software

[colisee]

One such identified software: git

[colisee]

In parallel, add LDAP2 based on decision taken on discord.

[ikke-t]

My thought would be to use yet another layer of build images. This would also solve some of the #171:

1. I'd add second php build image as an output layer. Layer 1) composer, 2) php build image 3) php output image
2. It would be perhaps easier to do just git archive|tar xf - for the given release in the php builder image. This way the SHA and such would come directly from local git command, no need for curl trickery.
3. I'd add composer build to the second layer. This layer could have whatever build tools needed
4. copy LB install directory to 3rd layer output image.

This would give freedom to do stuff on 2nd layer, install whatever tools needed to make image build more self sufficient (#171). Yet the output image would have the minimum set of installables and attack vectors. I dunno debian images enough, is there such smaller runtime base like UBI images for rhel/centos/fedora or alpines.

[ikke-t]

I did test Dockerfile with such layers. It dropped down the image size from 1.08G (with git still) to 0.95G. If someone knows what all apt-get installs are absolutetly needed in the runtime image could perhaps shave off some of that.