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/licenseInfo.mustache

@@ -0,0 +1,11 @@
+/**
+ * {{{appName}}}
+ * {{{appDescription}}}
+ *
+ * {{#version}}The version of the OpenAPI document: {{{.}}}{{/version}}
+ * {{#infoEmail}}Contact: {{{.}}}{{/infoEmail}}
+ *
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Do not edit the class manually.
+ */