[#15] Modification of scripts for adding/removing groups to projects and wrapper script

Changes have been implemented mainly in the addGroupToDrupalAdmins.sh script, so as to ignore the error that occurs when adding an existing group to a project (but also be able to catch other errors). The wrapper script can be executed with the following command so as to run in all projects of a cluster:

oc get projects -l okd.cern.ch/user-project="true" -A -o json --no-headers | jq -r '.items[] | .metadata.name' | xargs -I{} sh modifyGroups-wrapper.sh {}