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/model_doc.mustache

@@ -0,0 +1,41 @@
+{{#models}}{{#model}}
+# {{classname}}
+
+{{#description}}{{&description}}
+{{/description}}
+
+## Properties
+
+Name | Type
+------------ | -------------
+{{#vars}}`{{name}}` | {{#isPrimitiveType}}{{dataType}}{{/isPrimitiveType}}{{^isPrimitiveType}}[{{dataType}}]({{complexType}}.md){{/isPrimitiveType}}
+{{/vars}}
+
+{{^withoutRuntimeChecks}}
+## Example
+
+```typescript
+import type { {{classname}} } from '{{npmName}}'
+
+// TODO: Update the object below with actual values
+const example = {
+{{#vars}}
+  "{{name}}": {{{example}}},
+{{/vars}}
+} satisfies {{classname}}
+
+console.log(example)
+
+// Convert the instance to a JSON string
+const exampleJSON: string = JSON.stringify(example)
+console.log(exampleJSON)
+
+// Parse the JSON string back to an object
+const exampleParsed = JSON.parse(exampleJSON) as {{classname}}
+console.log(exampleParsed)
+```
+{{/withoutRuntimeChecks}}
+
+[[Back to top]](#) [[Back to API list]](../README.md#api-endpoints) [[Back to Model list]](../README.md#models) [[Back to README]](../README.md)
+
+{{/model}}{{/models}}