Enhance configuration
This is simply an elaborated rebase of @vladgo !6 (closed)
Each commit is as atomic as I could make it.
Unluckily I did not succeed at merging his branch on mine, to give him credit, as it's commit is too massive
Chart version is not updated, with progressive numbering it depends if any other MR gets merged before
It could be really useful open the wiki and publish the complete list of supported gitlab-runner Environment variables