Add support for non public S3 bucket

[goellner]

Is your feature request related to a problem? Please describe. Can't upload to private S3 Buckets, because value is hardcoded.

Describe the solution you'd like

statamic/core/Providers/FilesystemServiceProvider.php

Change this part:

    return array_merge($data, [
            'version' => 'latest',
            'root' => array_get($data, 'path', '/'),
            'visibility' => 'private',
            'credentials' => $credentials,
            'options' => array_get($data, 'options', []),
        ]);

to this:

    return array_merge($data, [
            'version' => 'latest',
            'root' => array_get($data, 'path', '/'),
            'visibility' => array_get($data, 'visbility', 'private'),
            'credentials' => $credentials,
            'options' => array_get($data, 'options', []),
        ]);