Use the RDB info fields to provide info to users.
Use the RDB info fields to provide info to users.

Fix #5790 and 5878.

Maybe a better option was to have such fields named with the first
byte '%' as those are info fields for specification, however now to
break it in a backward incompatible way is not an option, so let's use
the fields actively to provide info when sensible, otherwise ignore
when they are not really helpful.

JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis