refactor(types)!: remove handler and update docs (backport #17358) (#17366)

Co-authored-by: Julien Robert <julien@rbrt.fr>

server/mock/app.go

@@ -66,7 +66,7 @@ func NewApp(rootDir string, logger log.Logger) (servertypes.ABCI, error) {
 
 // KVStoreHandler is a simple handler that takes KVStoreTx and writes
 // them to the db.
-func KVStoreHandler(storeKey storetypes.StoreKey) sdk.Handler {
+func KVStoreHandler(storeKey storetypes.StoreKey) bam.MsgServiceHandler {
 	return func(ctx sdk.Context, msg sdk.Msg) (*sdk.Result, error) {
 		dTx, ok := msg.(*KVStoreTx)
 		if !ok {