DB v1.0.0-beta.1

`github.com/cosmos/cosmos-sdk/db` (cosmos-sdk/db here an after) is a module in the Cosmos SDK repository. It is used in `store/v2` instead of `tendermint/tm-db` which is now deprecated.

`cosmos-sdk/db` extends the `tendermint/tm-db` interface. however, it only supports BaggerDB and RocksDB (the databases we tested, which provide snapshot functionality necessary for store/v2 and ADR-040 implementation).