Add doctrine 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
- [x] check if this is something broadway wants to support
- [ ] write tests
- [ ] make it configurable in the bundle
There are good reasons (in ORM) to not use your guid as primary key... and my original PR was for the ORM implementation... Maybe it makes less sense for the other implementations...