[#80] storagegroup: Implement search query generator

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

pkg/services/object_manager/storagegroup/search.go

@@ -0,0 +1,14 @@
+package storagegroup
+
+import (
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+)
+
+// SearchQuery returns search query to filter
+// objects with storage group content.
+func SearchQuery() object.SearchFilters {
+	fs := object.SearchFilters{}
+	fs.AddTypeFilter(object.MatchStringEqual, object.TypeStorageGroup)
+
+	return fs
+}