We want to add an array of keys to be scanned to the zebra config so we can add them to the key storage at startup.

The keys field can be a vector of tuples Vec<(String, Option<height>)> where the first argument is the viewing key as a string and height is an optional birth date. Or it can just be Vec<String> if we want to add the birth height later.

Tasks:

• Add key list to zebra config. (New "scan" section)