community/docker-rootless-extras: move from testing

As discussed in the IRC yesterday I think it would make sense to move docker-rootless-extras from testing to community. Running docker without root is a sensible thing to do and documented in the alpine wiki(https://wiki.alpinelinux.org/wiki/Docker#Docker_rootless). The package is just a config file and the apkbuild. So it is very stable. User that want to run docker rootless should not need to enable the testing repo.