Allow importing / exporting from named Flysystem filesystem

[dkarlovi]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no
Branch?	master

In #344 we introduced importing from asset, which allows the user to seamlessly pull assets from a remote storage before the import happens. Using an artifact does the same when exporting.

An extension to this could be to allow import/export using an arbitrary Pimcore filesystem (not just asset) by doing something like

bin/console data:import (or export) -d 123 -p'{"file":"storage+storage1://some/path.csv"}'

Here, storage+storage1:// means:

1. storage+, use \Pimcore\Tool\Storage::getStorage
2. storage1, pass that as the name to 1.
3. use that storage instance to read / write the file some/path.csv directly to / from Flysystem

[dkarlovi]

Closing in favor of thephpleague/flysystem-bundle#96

See https://github.com/m2mtech/flysystem-stream-wrapper