Best way to indicate the funderIdentifierType when funderIdentifier is set up in the RIOXX2 workflow

[MicheleMorelli]

Hello,

as seen in #44 and #45 , Datacite needs that the funderIdentifierType is specified if the funderIdentifier element is present in the item's Datacite XML.

In #45 I have added a quick fix to this, but it needs to be improved as the funderIdentifierType value is currently hard-coded ("Crossref Funder ID").

The Datacite Schema 4.0 specifies that the value of funderIdentifierType should be picked from this list:
ISNI
GRID
Crossref Funder ID (as specified in the note, the current name includes ID)
Other

There are 2 potential approaches to deal with the value of funderIdentifierType:

1. adding a new RIOXX2 field and map that one;
2. doing some simple parsing to understand whether the funderIdentifier is an ISNI, GRID or crossref DOI, and set funderIdentifierType accordingly - otherwise set it to 'other'.

I reckon that the second approach seems to involve less potential ramifications and has a smaller scope, so I will try to implement it and put my fix in a pull request.