* add secondary storage usage monitor
* remove useless code
* code format & rename memory related metrics
* fix some bug
* use int64_t define file capacity & add init total_file_capacity
* use int64_t to define file_capacity
* rename memory usage related functions
* fix 2 bugs
* add docs
* fix code format
* add more docs
* use RAII way to update allocated_file_size
* fix ci
* fix CI compile problem