🚀 Feature: Method to Generate File URL

### 🔖 Feature description

Add `storage.getFileDownloadURL()`, `storage.getFilePreviewURL()`, and `storage.getFileViewURL()` methods.

### 🎤 Pitch

There are instances where it would be helpful to get a URL rather than the file as bytes such as when used by [`Image.network()`](https://api.flutter.dev/flutter/widgets/Image/Image.network.html) or on Flutter Web.

### 👀 Have you spent some time to check if this issue has been raised before?

- [X] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [X] I have read the [Code of Conduct](https://github.com/appwrite/appwrite/blob/HEAD/CODE_OF_CONDUCT.md)