Missing support for anonymous volumes

[klutchell]

The parser does not currently allow volumes without a source (anonymous volumes) even though the SV supports it at runtime.

balena-compose/lib/parse/compose.ts

Lines 471 to 482 in cd8e06e

	case 'volume':
	if (!serviceVolume.source) {
	throw new ValidationError('Missing volume source');
	}
	if (volumeNames.indexOf(serviceVolume.source) === -1) {
	throw new ValidationError(
	`Missing volume definition for '${serviceVolume.source}'`,
	);
	}
	if (serviceVolume.volume) {
	throw new ValidationError('Volume options are not allowed');
	}