ThreadPool: Refactor into several pools, with configurable types per pool #687
Description
Refactor the current single thread pool into several pools that can be used based on operation performed. This is handy for example to make sure search is only done on a specific thread pool since it associates resources per thread.
The new thread pools include:
index: for index/delete/bulk operations.search: For get/count/search operations.
Each pool can have a type associated with it, and based on the type, associated parameters. The types can be cached, fixed, scaling, and blocking.