[11.x] Add fromUrl() to Attachment

[KennedyTedesco]

The current Attachment::fromPath() method allows adding attachments from file paths, but it isn't immediately clear that URLs can be used with this method. This ambiguity could lead to confusion for users who want to attach files hosted on external URLs.

By adding the Attachment::fromUrl() method, the intent becomes explicit, improving the developer experience.

public function attachments(): array
{
    return [
        Attachment::fromUrl('https://host.com/files/file.pdf'),
    ];
}

Wdyt?