EZP-23328: Split IO interfaces

> [EZP-23328](http://jira.ez.no/browse/EZP-23328)
> Status: prototype / work in progress

## TODO
- [x] Prefix handling in Flysystem
- [ ] LegacyKernel MDH & BDH
- [ ] Prefix handling in LegacyKernel H
- [x] Prefix handling in LegacyDFSCluster MDH
- [ ] Flysystem BDH + tests
- [ ] Filesystem BDH test
- [ ] Look into ConfigResolver aware flysystem local adapter
- [ ] Create services in eZ/Publish/Core/settings, with an equivalent of the old filesystem