waddrmgr/db: store birthday block verification status
waddrmgr/db: store birthday block verification status

In this commit, we add a new key/value pair to the waddrmgr's sync
bucket to store the verification status of the birthday block. This
verification status determines whether the wallet has verified the
correctness of its birthday block through its sanity check on startup.

btcsuite/btcwallet,btcsuite/btcwallet