Add new element to reflect codelist category

[sargentfrancesca]

As per the codelist category update, add new metadata field to reflect the new categories in all codelists.

This can be completed as a script.

Please take into consideration versioning, and how codelists may have changed categories between versions.

Duplicate of IATI/IATI-Codelists#204

[Ocre42]

Blocked until the new category names are defined and the redefined list is updated