Update doc of ConsumerSettings#withBlocker

[bplommer]

See #582

[LMnet]

Do we really need to deprecate it? Maybe we could just add some additional information about requirements about thread-pool in the scaladoc. Because custom thread-pool may be useful for custom error handling, for logging, or to have good thread names.

[bplommer]

Do we really need to deprecate it? Maybe we could just add some additional information about requirements about thread-pool in the scaladoc. Because custom thread-pool may be useful for custom error handling, for logging, or to have good thread names.

I don't have a particularly strong opinion on this. It does raise another question though - if this is an ability we want to keep, should we also allow users of 2.x to provide custom ExecutionContexts for blocking operations?

[LMnet]

should we also allow users of 2.x to provide custom ExecutionContexts for blocking operations?

I think we should.

[bplommer]

I think we should.

I'm fine with that. So we'd have withCustomBlockingContext(ec: ExecutionContext) in the Settings classes (I think the word custom should be there because it's confusing if blockingContext can be None when a blocking context is always required). The fact that we have a Blocking abstraction should make it pretty easy to do, as in #584.

[LMnet]

Sounds good for me.

[bplommer]

I've revised this PR to just update the doc - I'll go ahead and merge.