Add ability to manually disconnect for Sftp driver

[hasfoug]

Exposed ConnectionProvider in SftpAdapter via geter, added disconnect method in SftpConnectionProvider

Related issues:
#1660
#1757

[frankdejonge]

Flysystem is not a DI, this should be removed.

[hasfoug]

@frankdejonge But how then i should call disconnect from SftpAdapter if ConnectionProvider is private? Do you suggest that we should rather add a public disconnect method in SftpAdapter as well?

[frankdejonge]

@hasfoug the connection provider is injected in, so you can get the same instance somewhere else.

[ttruong15]

@frankdejonge unfortunately the connection provider is injected in but for Laravel the way it's call the connection provider is a local variable and there's no way to access it.

Here's where it's being called:

vendor/laravel/framework/src/Illuminate/Filesystem/FilesystemManager.php

` /**
* Create an instance of the sftp driver.
*
* @param array $config
* @return \Illuminate\Contracts\Filesystem\Filesystem
*/
public function createSftpDriver(array $config)
{
$provider = SftpConnectionProvider::fromArray($config);

    $root = $config['root'] ?? '/';

    $visibility = PortableVisibilityConverter::fromArray(
        $config['permissions'] ?? []
    );

    $adapter = new SftpAdapter($provider, $root, $visibility);

    return new FilesystemAdapter($this->createFlysystem($adapter, $config), $adapter, $config);
}`

So here $provider is a local variable so we have no way off accessing the provider.  So if i want to expose the provider in Laravel I have to implement my own Storage system just to override this method to expose the provider. Such a pain.

[frankdejonge]

Superseded by #1763