Aggs: Add real memory CB call when building internal aggregators in buckets

[ivancea]

Related with #88128

This PR pretends to reduce the potential OOMs received when building internal aggregations.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[iverase]

Lets add parent in the method name so it is clear the purpose? like checkParentCircuitBreaker?

[ivancea]

I don't really understand what do we mean by "parent" here. We're updating the current CB. Parent of what?
That copied javadoc says parent too, but I'm not sure what it is

[iverase]

We have different circuit breakers with different thresholds. All those circuit breakers are below another breaker that is called the parent. In the past, the parent circuit breaker was a global threshold, so even if all CBs did not hit their individual threshold, summing them up will hit a global threshold (the threshold of the parent) and then the request would trip.

More recently, we introduced the real memory CB which replaced the parent circuit breaker (you can disable the real memory CB and you get the old behaviour). In this case, instead of checking a global threshold, we check the actual memory usage and will trip if we are over a threshold after trying to free some heap,

Therefore adding 0 bytes to the CB only has effect if we check the real memory, otherwise is a NOOP.

[ivancea]

@elasticmachine update branch

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	8.x