Fix the remaining issues with the datahub pipeline
This merge request addresses the two outstanding issues with the DataHub build pipeline running under GitLab-CI.
Firstly, the path where the docker images are published is updated to use the new scheme.
Secondly, the gradle commands have the web proxy options added, since these are not automatically picked up from the environment. Unfortunately, this means that all of the build stages must also be executed on trusted runners, since the shared sunners cannot access the web proxies.
Bug: T341194