Add support for new dynamic folder mode parameter on Cloudinary

[RandyCupic]

This PR introduces support for new dynamic folder_mode configuration that Cloudinary introduced (and is forcing on all new accounts), while still keeping support for the old fixed mode for projects that are currently using it. This can be configured:

netgen_remote_media:
    cloudinary:
        folder_mode: dynamic

Also this PR depends on it's parent PR (upgrading Cloudinary PHP API library form v1 to v2) because folder mode is not supported in v1.

TODO:

• properly test everything