nomad.yaml to provide user metadata

Currently the only way to provide user metadata is via the repo edit API. This is only used by the GUI to drive the edit dialog.

As an alternative we should think of a file format that allows to provide user metadata. This file could be passed along with uploads or uploaded later through an alternative POST-based edit API.

We should support a yaml and json format. It should allow to determine comment, references, coauthors, shared_with, datasets, and embargo settings.

provided with uploads

• this could either be a "nomad.yaml" file at the root and settings are applied to all mainfiles in subdirectories
• or also "nomad.yaml" files in subdirectories that override/extend the settings in higher directories
• the file could also have a list of settings based on mainfile paths that apply different settings to different calculations

provided through an edit api

• settings should be applied to all calcs matching a query
• or settings given to certain calcs via calc_id
• or settings given to certain calcs via upload_id+mainfilepath

use cases

• The most simply use-case would be uploaders provided dataset name, coauthors, references via a single file in their uploads.
• Added back-references when import data from a different database
• Maybe this could provide a mechanism to push data from an OASIS to central NOMAD via regular uploads