prototype "adaptive bulkhead" strategy

[Ladicek]

In the cloud world, statically defined bulkheads are not a great fit for limiting concurrency. We should add dynamic (adaptive) concurrency limiters, modeled after Netflix's https://github.com/Netflix/concurrency-limits.

I'm thinking "client-side" concurrency limiter would be a simple CDI interceptor, just like @Bulkhead (we could probably call it @AdaptiveBulkhead?). And we could also add a "server-side" concurrency limiter, which would probably be a few config properties and apply to the entire application.

eclipse/microprofile-fault-tolerance#474