feat: Make bloc_effects part of this repo

**Description**

The [bloc_effects](https://pub.dev/packages/bloc_effects) package from @DartAndrik should be part of the official bloc ecosystem like [bloc_concurrency](https://github.com/felangel/bloc/tree/master/packages/bloc_concurrency) and [hydrated_bloc](https://github.com/felangel/bloc/tree/master/packages/hydrated_bloc). The package solves the problems described here as effects in a common and handy way. It has the big advantage that you have to use less `BlocListner`s and things that have to be handled once (called effects here) do not dilute the state. I have often had the problem of overly complex states due to effects that had to be mapped in the state. The package helps a lot to structure code more clearly and to separate code parts from each other. It should therefore be shared with all developers and used accordingly in the tutorials. Adding the package to the bloc repo would help to do so.

**Desired Solution**

Contact the author of the package and, if possible, transfer the package to the packages folder of this repository so that maintanace and visibility are guaranteed.

**Alternatives Considered**

Develop an own official package to solve the problem.