Add ability for AIMDLimit to grow by a configurable amount

When AIMD works in conjunction with windowed limit, it might be way too careful in growing back after bursty spike (and, therefore, a backoff), because it has to proceed `window size` requests, before increasing limit by 1

My proposal is to add new method to AIMDLimit Builder, e.g.
```
public AIMDLimit.Builder growBy(int amount)
```
defaulting to 1 (current behavior)