Aggregations: Fixes scripted metrics aggregation when used as a sub aggregation

The scripted metric aggregation is now a PER_BUCKET aggregation so that parent buckets are evaluated independently. Also the params and reduceParams are copied for each instance of the aggregator (each parent bucket) so modifications to the values are kept only within the scope of its parent bucket

Closes #8036
Docs: Remove the note that fielddata doesn't support filtering.

This particular note was about fielddata filtering but could cause confusion
that fields that have doc values enabled cannot be used for filtering (as in
a `filtered_query`).
[CORE] Log if CircuitBreaker is tripping

Today we only throw an exception which might not be logged at all. This
commit adds debug logging if we are tripping a CB.

Closes #8050