Retrieve additional properties keys and values

Hello,

Is there an easy way to retrieve additional properties ?

```javascript
const Ajv = require('ajv');
const ajv = new Ajv();

const schema = {
"properties": {
"property1": {
"type": "string"
},
"property2": {
"type": "number"
}
},
"additionalProperties": true
}

const data = {
"property1": "Hello!",
"property2": 15,
"property3": "This is an additional property"
}

let validate = ajv.compile(schema)
let valid = validate(data)
```

Can I validate this data, then somehow obtain key & values of additional properties ?

Thanks !