updates and begin adding csv download

config/routes.go

controllers/data_download_controller.go

controllers/freezing_dates_controller.go

controllers/gdd_controller.go

docs/docs.go

docs/swagger.json

docs/swagger.yaml

go.mod

go.sum

models/cfs.go

models/csv.go

models/freezing_dates.go

models/gefs.go

persistence/entities/freezing_dates.go

persistence/entities/gdd.go

persistence/mongodb.go

services/data_download_service.go

services/freezing_date_service.go

services/nomads_service.go