Improving the clarity of ekf_localizer diagnostic

[Motsu-san]

Background

When the ekf_localizer diagnostics status is ERROR or WARN, it is not clear why or where it happens at a grance. We can get only that "localization: ekf_localizer" has "ERROR" in the header of diagnostic message.

Proposal

I've made the following pull-requests. This subdivides the diagnostic content to its checking item level.
I think there is little side-effect on dropping diagnostics message due to this increase of diagnostics contents.

Main

autowarefoundation/autoware_core#668

Associated changes

autowarefoundation/autoware_core#664
autowarefoundation/autoware_launch#1665
autowarefoundation/autoware_tools#309

Since I can't find a guideline of diagnostics content classification in Autoware documentation, I am open to any opinions or ideas so please feel free to comment in the threads.

[Motsu-san]

In TIER IV in-house discussion, There's the comments below,

• When the check are invalid, it is mis-readable to show that the check is unable to perform or the function for that purpose is not working by leveling "STALE", which means expiring confidence interval.
• So leveling ERROR or WARN with a key_value to show "invalid" seems to be better.

I've agreed them and modified the pull-request as said above.