How can i use merge array to a new array from a detail document
there is an example of data

**Example of result detail**

```
[{
    country: 'USA',
    val: 500,
    items: [
        {val:50, ...manyFieldsToIgnore},
        {val:30, ...manyFieldsToIgnore},
        {val:110, ...manyFieldsToIgnore},
    ]
}];

```

**Output expected**

```
{ items:[ 
    {
        country: 'USA',
        newNameValue: 500,
    },
    {
        country: 'USA',
        newNameValue: 50,
    },
    {
        country: 'USA',
        newNameValue: 30,
    },
    {
        country: 'USA',
        newNameValue: 110,
    },
};

```

im try to use $project and $concatArrays but i dont know how to set the new field(country) in details and change their key names

```
$project: {
    'root.country': '$country',
    items: concatArrays[ '$items'],
},
$project: {
    payments: concatArrays[ '$items', ['$root'] ],
}

```