Add v2 version to go module name

Replace all elements from `v2` to root directory.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

storagegroup/test/generate.go

@@ -0,0 +1,20 @@
+package storagegrouptest
+
+import (
+	refstest "github.com/nspcc-dev/neofs-api-go/v2/refs/test"
+	"github.com/nspcc-dev/neofs-api-go/v2/storagegroup"
+)
+
+func GenerateStorageGroup(empty bool) *storagegroup.StorageGroup {
+	m := new(storagegroup.StorageGroup)
+
+	if !empty {
+		m.SetValidationDataSize(44)
+		m.SetExpirationEpoch(55)
+		m.SetMembers(refstest.GenerateObjectIDs(false))
+	}
+
+	m.SetValidationHash(refstest.GenerateChecksum(empty))
+
+	return m
+}