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