CoR sweep param schema missing darks/flats loader params

Currently, this parameter schema is missing the darks/flats loader params: https://github.com/DiamondLightSource/imaging-workflows/blob/eb2fcaa2d01969fec25da4b4ed05d95a00d1ba25/httomo/schemas/cor-sweep-param.json#L102-L163

This means that if the user of the schema (such as tomohub) provides these darks/flats values, validation of the JSON object will fail, effectively causing these httomo loader parameters to not be usable with this workflow template.