zephyr/submanifests

This directory can contain additional west manifest files. Any files
in this directory will be included in the main west.yml file sorted by
filename.

See example.yaml.sample for an example.

For more details about how this works, see this part of the west
documentation:

https://docs.zephyrproject.org/latest/guides/west/manifest.html#example-2-2-downstream-with-directory-of-manifest-files