feat: support dynamic app db backend flag (#1226)

* support dynamic app db backend

* address pr reviews

* add comment

* Update server/start.go

Co-authored-by: Federico Kunze Küllmer <31522760+fedekunze@users.noreply.github.com>

server/flags/flags.go

@@ -7,13 +7,15 @@ import (
 	"github.com/spf13/viper"
 )
 
-// Tendermint full-node start flags
+// Tendermint/cosmos-sdk full-node start flags
 const (
 	WithTendermint = "with-tendermint"
 	Address        = "address"
 	Transport      = "transport"
 	TraceStore     = "trace-store"
 	CPUProfile     = "cpu-profile"
+	// The type of database for application and snapshots databases
+	AppDBBackend = "app-db-backend"
 )
 
 // GRPC-related flags.