provide a way to configure launcher-documentation location

[valdar]

If one need to point the backend to a different launcher-documentation location right now this file needs to be modified: https://github.com/fabric8-launcher/launcher-backend/blob/master/addons/launcher-addon/add-template-files.sh#L7 and the project rebuild.

Would be useful, specially during new boosters/runtimes development, to have this configurable at runtime with a configmap or changing the ocp template.