feat(openapi): Add modified typescript-fetch template

This template is modified from the original one, to handle multiple
status-code handling of response.

Don't ask me how they work, I don't quite understand them in depth...

openapi-template/allSagas.mustache

@@ -0,0 +1,19 @@
+import {all, fork} from "redux-saga/effects";
+
+import {
+{{#apiInfo}}
+{{#apis}}
+    {{#lambda.camelcase}}{{classFilename}}{{/lambda.camelcase}}AllSagas,
+{{/apis}}
+{{/apiInfo}}
+} from "./index{{importFileExtension}}";
+
+export function *allApiSagas() {
+    yield all([
+{{#apiInfo}}
+{{#apis}}
+        fork({{#lambda.camelcase}}{{classFilename}}{{/lambda.camelcase}}AllSagas),
+{{/apis}}
+{{/apiInfo}}
+    ]);
+}