the signer uses locks in GS [1] to manage jobs across a fleet of systems to provide reliability and automatic recovery from failures.  but some low level flakes in GS itself sometimes breaks us (see issue b/112110347 for details).

GS has a pubsub system which might be able to provide a lot of the same requirements and hopefully none of the flakes.  so we should investigate using that to manage the task queue.

[1] https://docs.google.com/document/d/1Yqv_G4QlMYOzJt9h_OU0564OAApPqekkTfFJI9cdJ-M/edit
[2] https://cloud.google.com/pubsub/docs/pull#pubsub-pull-messages-async-python