Summary:
Add support for IOTracing in blob files

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7958

Test Plan:
Add a new test and checked manually the trace_file for blob
files being recorded during read and write.

Reviewed By: ltamasi

Differential Revision: D26415950

Pulled By: akankshamahajan15

fbshipit-source-id: 49c2859b3a4f8307e7cb69a92704403a4da46d44