Kill commands on context cancelation
Gitaly is currently sending a SIGTERM to commands on context cancelation. This is done to give Git a chance to clean up any lock files and temporary files it may have created. There's no guarantee the command exits fast, or that it exits at all. To terminate the command immediately when context is canceled we should send a SIGKILL to it instead of a SIGTERM. We can do so once transactions are on by default as all of the temporary files will get cleaned up with the failed transaction.