Currently `migratewallet` migrates the address book (i.e. labels and
purposes) for watchonly and solvable wallets only in RAM, but doesn't
persist them on disk. Fix this by adding another loop for both of the
special wallet types after which writes the corresponding NAME and
PURPOSE entries to the database in a single batch.
Github-Pull: #26761
Rebased-From: d5f4ae7fac