Fix compute log tail regression which orphans tail processes
D1258 introduced a regression because in certain circumstances, the compute process killed the watcher process without killing the actual tail process.
This diff introduces signal handlers to kill the tail process when the watcher dies.
Ran solid that exited, made sure tail did not orphan... Also, ran solid that completed and killed tail watcher process, saw tail process terminate
Tracking implementation changes for better testing here: https://github.com/dagster-io/dagster/issues/1881
Reviewers: #ft, max, alangenfeld
Reviewed By: #ft, max, alangenfeld
Subscribers: alangenfeld, max
Differential Revision: https://dagster.phacility.com/D1335