How to build the starter locally

Doing a full .mvnw clean install fails, because I am missing the ee snapshots.

I have setup a settings-camunda.xml that I use via .mvn/maven.config … but it seems that it’s not enough to set

<repository>
          <id>camunda-bpm-ee</id>
          <name>camunda-bpm-ee</name>
          <url>https://app.camunda.com/nexus/content/repositories/camunda-bpm-ee</url>
          <releases>
            <enabled>true</enabled>
          </releases>
          <snapshots>
            <enabled>true</enabled>
          </snapshots>
        </repository>

a) What is the ee-snapshot repo?
b) is documentation available how to set up a local build? I only saw the CONTRIBUTING.md and that was rather vague.
b*) if not: I would like some docs …
b**) alternative: provide profiles for ee builds that are excluded by default or document how to run a local build excluding those modules.

Thanks
Jan