[Spike] Investigate WAL per Database solution

There is a way to encrypt individual records that related to some relation as every WAL record w/ data that has to flushed to the disk contains backup block which in turn contains RelfileLocator. But this would be potentially costly enterprise. Anyway I think it doesn’t make sense to go for it now. We can implement it later on (on top of current solution) if there will be such a demand. I see two option for the implementation:

1. Encrypt records while inserting them into WAL. That is more local way to do this but requires additional core changes.

2. Split the WAL’s byte stream into records and processing them while writing/reading it to/from disk. A bit clumsy but no need in additional core changes