[ISPN-DOCS] The Thread pooling should be documented

The default thread setting should be documented and the configuration should be explained with the limits (i.e. non-blockick >2*core makes no sense as it will end in decreased throughput.

For the other configurations

• thread-factory
• blocking-bounded-queue-thread-pool
• cached-thread-pool
• scheduled-thread-pool

there should be an explanation when it is used and what the limits/drawbacks are