Mark api/openapi-spec/**/*.json as generated files

Author: thockin

.gitattributes

@@ -10,4 +10,5 @@ test/test_owners.csv merge=union
 **/generated.proto
 **/types_swagger_doc_generated.go linguist-generated=true
 api/openapi-spec/*.json linguist-generated=true
+api/openapi-spec/**/*.json linguist-generated=true
 staging/**/go.sum linguist-generated=true