Add config_changed log for cachecheck

[matthewhilton]

Whenever the cachecheck re-pings, it should log a config change

This is so we can see the history of what updated the value and at what time

[brendanheywood]

When it is updating it has only seen the cached version, so lets also read from the db when it is about to update. This does two things:

1. it tells us if the db was already out of sync
2. it removes any possible read replica uncertainty

[brendanheywood]

Also not sure about config_log, maybe just error_log is enough. This will spam the config log daily