Add mechanism to synchronize and update services status

[danielSanchezQ]

This is a better and simpler approach than #29 . Responsibility is of the services implementations (With great power comes great responsibility) to understand the complexities of their services relationships.

How this works?

There is tokio::sync::watch channel handled by the service. Other services can subscribe and get updated requesting a watcher (watch::Receiver) from the calls in the overwatch_handle within services themselves.
Service status do not update automatically, I think is more flexible as service may chose to mark when they are ready to work. Also when they have finished its exection.

StatusHandle holds both parts of the sender/receiver parts of the watch channel and its clonable. That way the service can spawn tasks freely and send the handle to handle internal status as well.

[danielSanchezQ]

Still missing documentation. Will be adding that next.

[youngjoon-lee]

Thank you! Looks good! I just left a question below.

[al8n]

🚀