Refactor farm calendar json-ld converter to use Calamus

[fedjo]

Change the converters/farm_calendar_to_json.py- script to dynamically create the JSON-LD representation using calamus

• Models and Serializers should be define there

• Use as input examples/generic_farm_calendar_v2_enhanced.json

• Examples of extracted JSON-LD can be found in converters/generic_farm_calendar_v2_AIM.jsonld

[rapw3k]

hi @fedjo who is responsible for this?