This tree contains additional configuration which happens "pre deployment",
e.g before the OpenStack services themselves are configured but after the
nodes themselves have been provisioned and initially configured.
Typically for puppet deployments these additional configs will put in place
hieradata which is then consumed by the subsequent puppet configuration
which occurs during the post-deployment phase.
If you need to specify multiple configs, you can chain them together in a
template, see the multiple.yaml example:
OS::TripleO::ControllerExtraConfigPre: puppet/extraconfig/pre_deploy/controller/multiple.yaml
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