related: #42803
1. add a new thread pools using folly::CPUThreadPoolExecutor, named by
FThreadPools
2. reading vectors from chunkcache will use the separated
CHUNKCACHE_POOL to avoid being influenced by load collection
3. Note. For safety on cloud side on 2.5.x, only read-chunk-cache
operations is using this newly created thread pools other caller points
for threadpool will be mutated in the near future
4. master-branch doesn't need this pr as caching layer unified the chunk
cache behaviour
Signed-off-by: MrPresent-Han <chun.han@gmail.com>
Co-authored-by: MrPresent-Han <chun.han@gmail.com>