Summary:
`enable_custom_split_merge` is added for enabling the custom split and merge feature, which split the compressed value into chunks so that they may better fit jemalloc bins.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10690
Test Plan:
Unit Tests
Stress Tests
Reviewed By: anand1976
Differential Revision: D39567604
Pulled By: gitbw95
fbshipit-source-id: f6d1d46200f365220055f793514601dcb0edc4b7