So for the coming release, Helm charts will be cloud-agnostic templates. This means if you choose to use GKE, you will need to configure the relevant resources from GKE in the helm charts templates provide by Atlassian and then set up GKE cluster correctly by yourself.
We are trying our best to provide examples for references but noted that they are not officially supported by us yet. And you are always more than welcomed to come to this group to share your know-how and questions.