Ampli CLI generate invalid Swift code when an identifier starts with a number

In my case the product manager defined a property called `1Year`. In this case amply generate the following enum

```
public enum Duration: String {
case 1Year = "1Year"
}
```

`1Year` is an invalid swift identifier.

Ampli should generate a valid identified by prefixing the value stating with a number by a valid character, for example `case _1Year = "1Year"`