feat: Implement get role mappings API endpoint

packages/backend/src/serializers/role-mapping.ee.js

@@ -0,0 +1,10 @@
+const roleMappingSerializer = (roleMapping) => {
+  return {
+    id: roleMapping.id,
+    samlAuthProviderId: roleMapping.samlAuthProviderId,
+    roleId: roleMapping.roleId,
+    remoteRoleName: roleMapping.remoteRoleName,
+  };
+};
+
+export default roleMappingSerializer;