sync: devspace sync command behavior

[FabianKramm]

Currently devspace sync will delete locally not existing files in the remote folder. While this behavior makes sense for devspace dev and can be configured with the downloadOnInitialSync flag there is no option for the devspace sync command. We should introduce a flag --download-on-initial-sync so users are able to configure such behaviour

[LukasGentele]

Completely agree. I even think that --download-on-initial-sync should be true by default because using false does not just mean not downloading files, it would also mean deleting remote files if they are not existing locally and that is a very common scenario but deleting the files is very rarely intended.