* [project-history] skip HEAD on blob without file-hash
* [project-history] only 404s indicate a missing blob
* [project-history] error checking for existing blob is fatal
* [project-history] always skip creating blob if already exists
Ignore createdBlob detail after performing check on blob. It might not
exist on old operations that have been queued.
* [project-history] fix unit tests
* [project-history] migrate test to new fetch call
GitOrigin-RevId: 457963042e9d836647d3c122516329d4dc9b544f
