Custom pool implementation with telemetry

[chasers]

Replace poolboy with custom pool implementation:

• [ ] better support idle_timeout (database_idle_time)
• [ ] telemetry events
• [ ] min_idle_workers - ensure a minimum count of workers are started and available - useful when startup time of a worker is costly - how many additional idle direct connections ready inside pool always
• [ ] should be parition-able
• [ ] workers should only be allowed to be checked out based on some criteria or state
• [ ] don't Supervisor.terminate_child in process loop, do async

Maybe fork: https://github.com/general-CbIC/poolex