Enable cpu throttle for indexer by default

By default, indexer is configured to use all cores on a box. With a high mutation/scan workload, indexer node can run at constant CPU saturation. This can lead to auto-failover of the node being triggered if indexer doesn't respond to ns-server heartbeat within stipulated time.

This has been enabled in master branch due to auto-failovers seen in volume tests e.g. MB-55471.

Config
"indexer.cpu.throttle.target"

The perf impact needs to be assessed with the perf tests.