add watchdog http server

[musitdev]

Add a http server that return the codes:

• Alive => StatusCode::OK (200)
• Graceful => StatusCode::NO_CONTENT (204)
• Critical => StatusCode::SERVICE_UNAVAILABLE (503)

2 signals are implemented:

• the scheduler loop doesn't run
• the mempool has more than 0 Tx after pooling.

Add a timer to detect that the mempool pick a task is not called after a certain time.

[musitdev]

I've still some change. I reopen a new PR.