Improve StringMap typing in jami-swig

Change-Id: I3773d7353878de9f5f01f957287afe48c6977e8b
diff --git a/server/src/interfaces.ts b/server/src/interfaces.ts
new file mode 100644
index 0000000..6131426
--- /dev/null
+++ b/server/src/interfaces.ts
@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2022 Savoir-faire Linux Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with this program.  If not, see
+ * <https://www.gnu.org/licenses/>.
+ */
+export interface Constructable<T> {
+  new (): T;
+}