Reject request that exceeded limit with TooManyRequestsRejection

[unoexperto]

Reject request that exceeded limit with TooManyRequestsRejection rejection instead of responding with complete directive. Rationale is to allow developer to respond with body he/she wants (in custom rejection handler) instead of hardcoding text-only response.

Downside of this method is that there is no default handler for this rejection similarly to handler for TooManyRangesRejection for example. So if library user doesn't implement handler for TooManyRequestsRejection http client will get 500 error.

For example in my case all rejections are wrapped into json response that mobile client understands.

[yeghishe]

@unoexperto The idea is interesting. I do think that the default behavior should be for library to handle it and make it as transparent to developer as possible. On other end I'm all for allowing dev to have control when needed. There is ThrottleSettings as an implicit parameter for the method you're trying to change. I would say we can add more settings for this kind of things.

There is also ConfigMetricThrottleSettings.scala where the settings can be injected from typesafe config.

Let me know what you think