Improve log messages to help debug worker timeouts

[cjlarose]

Is your feature request related to a problem? Please describe.

Users sometimes encounter Terminating timed out worker messages in puma logs. These messages are generated in one of two cases:

1. an already-booted worker failed to report itself to the master process within the last worker_timeout seconds (default 60)
2. a new worker failed to boot within worker_boot_timeout seconds (default 60).

If a user is getting these messages in the log, it's not really clear which situation they ran into and makes it harder to diagnose the problem. See #2527 for an example

Describe the solution you'd like

1. Log messages should clearly indicate if a worker boot timed out or if a worker failed to "check-in" after boot

Example:

• Terminating timed out worker (worker failed to check in within 60 seconds): 2006
• Terminating timed out worker (worker failed to boot within 60 seconds): 2008

2. The other thing that would be nice is just writing to the logs the amount of time that it look to boot a worker (when it was successful)

• Worker 0 (pid: 20934) booted in 12.34 seconds, phase: 2

This would be useful to help operators know if their workers are booting close to the timeout threshold or not