CDS does not set config_reload or config_reload_time_ms statistics

[isker]

This page documents xDS statistics. It seems that each kind of resource supported by xDS must update config_reload and config_reload_time_ms itself, and CDS simply does not do this. I see rds, scoped rds, and vhds doing it. CDS (and others?) are missing. I am concretely aware of CDS missing it, because we use CDS and RDS, and only have these statistics for RDS.

The update_* stats documented on the same page do not have this problem, as they are done centrally for all resources.

[adisuissa]

Thanks for raising this issue!
Seems this was not added for some of xDS subscriptions.
PRs are welcome.