EZP-23390: IOService loads whole file to get mime type with FS cluster handler

https://jira.ez.no/browse/EZP-23390

Todo:
- [ ] Get [legacy PR](https://github.com/ezsystems/ezpublish-legacy/pull/1082) merged and change composer.json to reflect that before merging this
imho waste of time as this is built using IOFactory, and other handlers built in this does not need it. And from what I can see InMemory can be removed by now.