This adds the field data circuit breaker, which is used to estimate
the amount of memory required to load field data before loading it. It
then raises a CircuitBreakingException if the limit is exceeded.
It is configured with two parameters:
`indices.fielddata.cache.breaker.limit` - the maximum number of bytes
of field data to be loaded before circuit breaking. Defaults to
`indices.fielddata.cache.size` if set, unbounded otherwise.
`indices.fielddata.cache.breaker.overhead` - a contast for all field
data estimations to be multiplied with before aggregation. Defaults to
1.03.
Both settings can be configured dynamically using the cluster update
settings API.
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