Set both custom error code and custom message inside custom function

### Runtime

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### Runtime version

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### Module version

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### Used with

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### Any other relevant information

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### How can we help?

```js

const myCustomFn = (value, helpers) => {
// If condition is matched I want to set both code 'my.error.code' and message inside this myCustomFn
// but helpers.error() does not allow setting message and helpers.message() does not allow setting code other then "custom"
// and I do not want in many places in code use .custom() with combination .messages() because messages will be repetitive:
// .custom(myCustomFn).messages({ 'my.error.code' : 'My error message' })
// I tried to use helpers.prefs.messages['my.error.code'] = 'My error message' but it causes error
if (.........)
return helpers.error('my.error.code');

return value;
};

joi.object({
.........
})
.xor(.......)
.custom(myCustomFn)
```