Switch from `master` to `main` as default branch

[nickboldt]

"Red Hat is committed to replacing problematic language in our code, documentation, and web properties. We are beginning with these four terms: master, slave, blacklist, and whitelist. Because of the enormity of this endeavor, these changes will be implemented gradually over several upcoming releases."

Can we switch this repo over to main as its default branch too? Perhaps before the first official DWO release ?