Validates a variable which has a length property (e.g. a string) against the minimum length provided
     
MinLengthValidator is used by DataValidatorListener for validating data objects.
     
     An attribute of a data model may define a min length in validation properties:
     
     {
        "name": "model",
        "title": "Model",
        "description": "The model of the product. Use with the URL of a ProductModel or a textual representation of the model identifier. The URL of the ProductModel can be from an external source. It is recommended to additionally provide strong product identifiers via the gtin8/gtin13/gtin14 and mpn properties.",
        "type": "Text",
        "validation": {
            minLength:4
        }
    }
     
     An operation tries to save a data object:
     
     var obj = {
                "model": "FS2",
                "name": "USB 3.0 Adapter"
            };
     context.model("Product").save(obj).then(function() {
               return done();
           }).catch(function(err) {
               return done(err);
           });
     
     
     Result:
     
     {
        "code": "EMINLEN",
        "model": "Product",
        "field": "model",
        "message": "The value is too short. It should have 4 characters or more."
    }