Add doctrineORM readmodel support

I'm already using this in my projects. (Although I'm considering using only dbal)
Before I write unit tests I want to make sure you guys want to add this to this library.

Todo
- [ ] check if this is something broadway wants to support
- [ ] write tests
- [ ] make it configurable in the bundle
The interface doesn't have a second argument flush. I know you can add arguments with default values (despite the interface) but IMO it should default to 'true' then.