Fix handling of Mutable options; Allow DB::SetOptions to update mutable TableFactory Options (#7936)

Summary:
Added a "only_mutable_options" flag to the ConfigOptions.  When set, the Configurable methods will only look at/update options that are marked as kMutable.

Fixed DB::SetOptions to allow for the update of any mutable TableFactory options.  Fixes https://github.com/facebook/rocksdb/issues/7385.

Added tests for the new flag.  Updated HISTORY.md

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7936

Reviewed By: akankshamahajan15

Differential Revision: D26389646

Pulled By: mrambacher

fbshipit-source-id: 6dc247f6e999fa2814059ebbd0af8face109fea0