[Design] Health Checker Function for Autoware

[hakuturu583]

Now, Autoware has diagnostic_lib for diagnostics.
But, I think it is not enough.

1. Hardcoded diagnostics function and config files is necessary.
2. No error level
3. Cannot know when the error status recover.

So I want to re-resign Health Check functions for Autoware.

Design

Autoware Health Checker Provides in ROS and out ROS diagnostics.

[kfunaoka]

@hakuturu583 As discussed yesterday, would you create README.md and answer @sgermanserrano 's question autowarefoundation/autoware#2058 (comment)? Here might be the best place to Q&A. It will help all Autoware developers.