[keyserver] Introduce yarn clear-profile-logs to keyserver

Summary:

1. We set output_dir of profiling data to cpu_profiling_logs/
2. We add cpu_profiling_logs to .gitignore so we don't clutter our workiing copy
3. We introduce a yarn clear-profile-logs command that rm -rfs cpu_profiling_data

Depends on D9302

Test Plan:

1. Made sure that profiling data for new profiling sessions were within cpu_profiling_logs
2. Made sure profiling data added to cpu_profiling_logs was ignored by git
3. Made sure yarn clear-profile-logs removed everything from cpu_profiling_data

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D9303