Issue #3249252 FTP fetcher for Drupal 9|10

Users want to have an FTP fetcher out of the box. I have built an FTP fetcher plugin including a configuration form. The user can insert the host, port, username, password, and file path in the form and the fetcher will use these settings to connect to an FTP server. The fetcher depends on the flysystem filesystem library and the drupal key module to store the password in a secure way.