Add user-defined metadata for Zenodo

I'm not sure if this is within the scope of facile-rs, but it would be great to have the option to add user-defined metadata to Zenodo records. This would make facile-rs more universally usable with Zenodo.

One example: I have a project in which I want to upload the content of the repository to Zenodo in a CI pipeline. I'm not using codemeta.json in my project, but have information stored in CITATION.cff. I can easily convert this to codemeta.json with cffconvert and then use facile-rs, but I would have to

1. manually edit the codemeta.json to add additional information and
2. check the facile-rs code to see which fields of codemeta get translated to which Zenodo field.

Having an additional argument in the create zenodo function that takes a json string (or path to a json file?) and adds the content of this argument to the variable zenodo_dict after populating it automatically from the codemeta.json, this would be very handy. With this argument I would be able to add metadata I know from the Zenodo API without understanding which field of the codemeta file gets translated to which Zenodo metadata field. And I could also easily add information for Zenodo which are currently not considered by facile-rs (e.g. grants or a custom upload_type of the resource).

I think I could propose some code if you are interested in adding this to facile-rs.