(PUP-1433) Add example environment to deb packages

This adds an /etc/puppet/environments/example_env directory,
subdirectories, and a README about the environment. We can't remove the
existing /etc/puppet/manifests directory because it would destroy a
large number of deployments (anyone with automation depending on that
directory being created). We also can't create a production environment
because it would then shadow the /etc/puppet/manifests directory and
also end up breaking automation as well as any existing regular
installations. The example environment with a README seems to be the
best way to move forward and try to present the new system to users.