Feature: enable excluding file from backup

## Feature Request
Enable excluding file from backup.

### Plugin

capacitor-filesystem

### Description

This is a feature that is a good practice for directories like DATA, for files that are redownloable. Only implementation for iOS. https://developer.apple.com/documentation/foundation/urlresourcevalues/isexcludedfrombackup

For Android, it can be made at project level, with something like `android/app/src/main/res/xml/backup_rules.xml`:
``` android/app/src/main/res/xml/backup_rules.xml

```

And on `AndroidManifest.xml`:
```

```

Not needed implementation for web.

### Platform(s)

iOS

### Preferred Solution

I opened a PR with my solution.

Not sure if it's interesting to add the info about Android.

### Alternatives

### Additional Context