Add possibility to customize coffea-casa/coffea-casa-analysis Dask worker image

[oshadura]

For https://github.com/CoffeaTeam/coffea-casa/tree/master/docker/coffea-casa-analysis we will develop probably a solution that will allow easily customise or overwrite exisring in image UNL HTCondor settings

[clundst]

This requires the overhaul of the helm charts which is a different issue.