Consumer max rate tests

[timfox]

I'm wondering how these pass, since we haven't implemented consumer rate limiting yet

[clebert.suconic]

I have added some implementation.. I was going to post about it today.


If you think the implementation is wrong... we could revert the tests.

[timfox]

Ok, that's fine, as long as you're confident there are no nasty side effects such as messages building up in the client side buffer