Add `MonadYield`

```haskell
class (Monad m) => MonadYield o m | m -> o where
yield :: o -> m ()
```

[pipes](https://hackage.haskell.org/package/pipes) and [conduit](https://hackage.haskell.org/package/conduit) could have instances. It shouldn't be added here however until another more basic instance exists in transformers, which would be useful anyway since those two packages require mmorph and mono-traversable, respectively. Consider this issue also a discussion for the transformers instance.

@snoyberg has opined about the need for a more central streaming abstraction in [this blog post](https://www.snoyman.com/blog/2020/12/haskell-bad-parts-3/). What are people's thoughts about a streaming type in the core libraries? In base?

cc @Gabriella439