Automated ingestion via `yml` files upstream

Originally here: https://github.com/marda-alliance/metadata_extractors_registry/issues/7

> Potential idea as discussed: save `.marda.yaml` as a file in a GitHub repo that outlines the entry in this registry, then simply submit the link to the repo here.
>
> Repo can then be watched by the CI of the registry and entries updated.
>
> Can also make a form/UI for creating the initial yaml file.