New option to create subfield with desired content

[aatuny]

createFrom action needs a new option that allows new subfield to be created with desired content.

Example case:
Source record has a 776 field that is used to create 020 field to result record. We would like to add a $q subfield with content 'PDF' to it.

Source record:
77608 L $$iVerkkoaineisto (PDF):$$z9786191920372

Desired outcome to result record:
020 L $$a9786191920372$$qPDF

Example conf:
"776": { "action": "createFrom", "options": { "convertTag": "020", "ind1": " ", "ind2": " ", "subfields": { "z": { "convertCode": "a", modifications: [ hyphenate ] }, "q": { "createNew": true, "data": "PDF" } } } }