EZP-23328: Implement DFS IO handler

> [EZP-23328](https://jira.ez.no/browse/EZP-23328)
> Status: works, but with many todo

This (big, sorry) PR adds a DFS IO handler.

### Features
- Separates BinaryData and Metadata handlers
- Comes with a Flysystem binarydata handler that handles many storage backends (local, s3, dropbox...)
- Has a front-controller that serves local files like the old index_cluster.php
- URL decorators: can modify an URL to a binary file, for instance to serve static assets using another server, or to serve files from aws-s3 directly
- Semantic config, where different io handlers can be assigned to different scopes

### TODO
- [ ] Write list of tasks