extract more structured data from ESAC registry

[maxheld83]

currently, a lot of the ESAC registry data appears to be somewhat unstructured. To better make use of this data in #240 #243 et al, it would be good to clean this data and expose it as an R object in {hoad}.

In addition:

• we should get the data programmatically from ESAC #244.

• clean some fields (ie. yes, no should be logical, etc.).

• [ ] publisher is an open text field, and would have to be checked against some definitive list

• [ ] agreement_url is an open text field

• [ ] consortia/institution is an open text field

• [ ] access_costs should be ordinal

• [ ] worfklow_assessment are 3 separate vars!

• [ ] article_types can be parsed down to a few types (that need not be an open field)

• ...