Add memory circuit breaker

[jngz-es]

I'd like to add memory circuit breaker on LTR memory usage to not impact the cluster availability, like ingestion function, when the system memory usage is high.

[nathancday]

This seems like a smart thing to do, what would be the behavior when memory usage is too high?

[jngz-es]

What I am thinking is rejecting APIs which consume memory like create model/feature set etc.