Creating a repo is self-service, but pay attention and change the default configuration of the notifications so that email goes to issues@openwhisk.apache.org and not to dev@openwhisk.apache.org. Also note that the tool will automatically inject "incubator-openwhisk" into the repo name, so don't do it yourself and get a redundantly long name.
You create the repo here https://gitbox.apache.org/setup/newrepo.html.
After the repo is created, you need to open an INFRA JIRA ticket to get it properly configured. For an example ticket, look here: https://issues.apache.org/jira/browse/INFRA-17095