Add support for mounting/syncing iCloud drive on Linux

[ryuheechul]

Currently there is no such support on Linux platform according to https://support.apple.com/en-ca/guide/icloud/mm203b05aec8/icloud

This makes the experience of syncing files between Linux and other Apple devices very poor. Instead of a Dropbox style experience, users have to upload and download files manually through a browser. Apple opened up to Windows already and I believed the same can be and should be done for Linux platform as well.