Parasails custom error handling

**Node version**: v14.15.1
**Sails version** : 1.4.0
**Parasails**: v0.9.2
**ORM hook version** : 2.1.1
**Sockets hook version** : 2.0.0
**Grunt hook version**: 4.0.0
**DB adapter & version**: 1.0.1
**Vuelidate**: v0.7.6

### Description
Hello!

I integrated vuelidate for client form validations with Sails, it works perfeclty with the validations that the plugin comes with out of the box, but when I try to add a custom validation the way the error works is by **resolving or rejecting a promise**, take a look a the [example](https://vuelidate.js.org/#sub-asynchronous-validation)

Here is a short example of what I'm currently doing:
```javascript
parasails.registerPage('create-legal-process', {
mixins: [window.vuelidate.validationMixin],
data: {
// we should define formData equal to the form in 'validations'
formData: {
code: ''
},

},

validations: {
formData: {
code: {
// the 'required' validation works, it comes out of the box
required: validators.required,

// this is a custom async validation, I'm using throttle to reduce the amount of requests
isUnique: _.throttle(async (value) => {
if (value === '') {
return true;
}

// query language for sails api
var params = {
where: JSON.stringify({
code: value
})
};
// perform request
var { data: process } = await axios.get('/legalprocess', { params });

// if the list isnt empty then throw error
if (legalprocess.length > 0) {
throw 'There\'s a legal process with that code already.';
} else {
// if it works just return anything that resolves correctly
return 'That code isn\'t being used yet.';
}
}, 1000),
},
},
},
});
```

### Expected behavior
I would like to throw errors in a way that I can continue to use this plugin, maybe throw an error with a specific code like `E_CLIENT_VALIDATION` that can be tolerated so that it doesn't display the error overlay, but if there's any **workaround** I'd like to know.

Thanks for your time, I love Sails!

Start with the parasails.registerPage example in the issue and review Vuelidate's asynchronous validation behavior, especially how rejected promises are surfaced. Then trace how Parasails handles the resulting client-side error and compare it with the requested E_CLIENT_VALIDATION behavior; done means the supported handling or workaround is documented and the error no longer shows the unwanted overlay.

Written by the indexing model from the issue text.