json-ld: Raise custom error if json file for output configuration is missing

[alastair]

We have a test to try and load a config from a mapping file:

ce-api/src/routes/helpers/transformers.js

Lines 39 to 43 in 1e669bf

	const config = require(`./jsonld/${type}.json`)
	if (!config) {
	throw new Error(`JSON LD not supported for type "${type}"`)
	}

however the require will fail with an exception if the file is missing and we don't get our custom "JSON LD not supported for type" error message