Add RedistributingCircuitBreakerService

Adds a breaker for request BigArrays, which are used for parent/child
queries as well as some aggregations. Certain operations like Netty HTTP
responses and transport responses increment the breaker, but will not
trip.

This also changes the output of the nodes' stats endpoint to show the
parent breaker as well as the fielddata and request breakers.

There are a number of new settings for breakers now:

`indices.breaker.total.limit`: starting limit for all memory-use breaker,
defaults to 70%

`indices.breaker.fielddata.limit`: starting limit for fielddata breaker,
defaults to 60%
`indices.breaker.fielddata.overhead`: overhead for fielddata breaker
estimations, defaults to 1.03

(the fielddata breaker settings also use the backwards-compatible
setting `indices.fielddata.breaker.limit` and
`indices.fielddata.breaker.overhead`)

`indices.breaker.request.limit`: starting limit for request breaker,
defaults to 40%
`indices.breaker.request.overhead`: request breaker estimation overhead,
defaults to 1.0

The breaker service infrastructure is now generic and opens the path to
adding additional circuit breakers in the future.

Fixes #6129
Yep! Good idea :)