Summary: Add mutable options info into `OptionsTypeInfo` and use it to parse mutable options map. Also support `max_bytes_for_level_multiplier_additional` in option file.
Test Plan: unit test
Reviewers: yhchiang, IslamAbdelRahman, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D63843