Is there a way to set global joi config?
I want to set joi `allowUnknown` as a global config, because I don't mind what additional fields are passed in as long as the fields I want are supplied.
I have to set `allowUnknown` in every Joi valid code, is there a way to set global Joi config like this below?

```js
const router = require('koa-joi-router');
const pub = router({
  validate: {
    allowUnknown: true,
  },
});
```