Need A Way To Throw Network Error

## 🏗 Enhancement Proposal

### Pitch

In fact, we always need a way to throw out our errors when our image requests fail, but we're difficult to do this now. What we can do is just throw an error like this, but this is certainly not what we want.

```dart
CachedNetworkImage(
imageUrl: 'https://xxx.com',
errorWidget: (context, url, error) {
throw error;
},
),
```

This is a bad implementation, and it may cause our errorWidget to display an exception. I think that network errors should be thrown from inside the component and caught by A at the business level. This will help us in error handling and error collection. The outer api should look like the following.

```dart
try {
CachedNetworkImage(
imageUrl: 'https://xxx.com',
errorWidget: Icon(Icons.error),
),
} catch(e) {
// something to do in error
throw e;
}
```

Thanks.

### Platforms affected (mark all that apply)
- [x] :iphone: iOS
- [x] :robot: Android