Field "is_verified" dump permissions

[alejandromumo]

          Zenodo does not dump the field, therefore is not visible in API queries.

Ideally, we could protect the field and only make it visible to admins. However, it would "pollute" a bit of the record's namespace by introducing user-related permission.

Options:

1 - Do not dump the field at all (I don't see why not)
2 - Add a permission to dump it (e.g. AdminAction(user_management_action))

WDYT?

Originally posted by @alejandromumo in #1399 (comment)