Preview: Improve cache-hit of dev/preview:build

[mads-hartmann]

Currently the "cache hits" for leeway build in a Workspace is not the same as in Werft - leeway wants to build a lot more packages when executed in a Gitpod workspace

Screenshot of Leeway plan in Werft

Screenshot of Leeway plan in Gitpod workspace

To reproduce, run the following from a branch in a workspace

gcloud auth login --no-launch-browser
time leeway build -Dversion=test -DSEGMENT_IO_TOKEN="" --dry-run

I suspect it's due to missing build argument or other differences between how leeway is invoked in Werft vs. workspaces. Find the right leeway invocation and update dev/preview:build to use that invocation.

---

This is a follow up from when working on https://github.com/gitpod-io/ops/issues/5766