edit files: allow users to modify files for non-zenodo DOIs

[alejandromumo]

We want to allow a set of users to edit files for Non-Zenodo DOIs.

Discussed with @slint and agreed on implementing something similar to the media files edition, i.e. we create an action to manage files and then create a role associated with the action. Lastly, we add this role to specific users so they can modify the files.

When this is deployed, we still need to create the role in production and associate the users:

$ invenio roles create files-manager
$ invenio access allow manage-external-doi-files role files-manager
$ invenio roles add <user_email> files-manager