Support building without passing commandline arguments on the shell

[codingchili]

Because when using docker we dont want to execute any commandline on the zapperfly-server host. The build script should be saved in the build directory before the build is started with a known filename. This allows us to use a static and secure commandline for launching containers.

[codingchili]

Build scripts are now passed in a shared volume - but only for docker builds. Normal builds don't benefit from this.