Proposal: Add support for fetching meta/userdata from directory

[silentirk]

We use cloudbase-init not only for cloud instances, but also for baremetal server installations and pre-seed config data during server deployment.
It would be good to have an option to put it into some directory to avoid creation of a separate partition, which is not handy in some situations. Similar to a cloud-init way, where config data may be pre-seeded in /var/lib/cloud/seed/nocloud/

Some implementation can be seen here:
https://review.opendev.org/c/x/cloudbase-init/+/881789