Provide logging and status checking on WorkerDispatcher._subprocess

i04 was recently seeing a 504 gateway timeout when triggering BlueAPI from GDA. Following the stack of logs, it seems like BlueAPI was hanging after successfully receiving a POST request (for submitting a task).

The most likely cause of this hanging appears to be an issue with Blueapi's `WorkerDispatcher._subprocess`. However, there is currently no way to get information about its status. It would be useful to add a way to get the status of this subprocess (maybe a heartbeat?), as well as some logging

## Acceptance Criteria
- Logging statements added for this subprocess, as well as a way to get its status