Investigate endpoint response time: get blame information

As the result of investigation of which API endpoints should be added to Performance Toolkit, we need to investigate this endpoint:

• GET /projects/:id/repository/files/:file_path/blame

API doc: Allows you to receive blame information

Why it should be investigated: according to data from customers this endpoint appears to be slow:

• Called: often(0.5%), Response time: very slow (perc95 = 6788.99 ms). Also methods Projects::BlobController#update and Projects::BlobController#destroy are slow as well(perc95 =43787.05 ms)

• Investigate endpoint

• Create an issue for a fix if the endpoint is slow