Upgrade yq to v4

[FlorianHockmann]

We're using yq to configure the YAML config file for Gremlin Server, but we are still using version 3 of that library. We should update it to version 4 to stay on a supported version.
This is most likely a breaking change as the syntax changed between both versions: https://mikefarah.gitbook.io/yq/upgrading-from-v3