js-api: Add hooks to run tests and render docs of JS API examples.

This commit adds python code to call javascript_examples.js in its
two supported modes. tools/test-api asserts that the example output
is as expected, whereas the API markdown extension is used to render
these examples in the docs.

zerver/openapi/javascript_examples.py

@@ -0,0 +1,26 @@
+import os
+import json
+import subprocess
+
+from zulip import Client
+from zerver.openapi.openapi import validate_against_openapi_schema
+
+def test_js_bindings(client: Client) -> None:
+    os.environ['ZULIP_USERNAME'] = client.email
+    os.environ['ZULIP_API_KEY'] = client.api_key
+    os.environ['ZULIP_REALM'] = client.base_url[:-5]
+
+    output = subprocess.check_output(
+        args=['node', 'zerver/openapi/javascript_examples.js'],
+        universal_newlines=True,
+    )
+    endpoint_responses = json.loads(output)
+
+    for response_data in endpoint_responses:
+        print(f"Testing javascript example: {response_data['name']} ...")
+        validate_against_openapi_schema(response_data['result'],
+                                        response_data['endpoint'],
+                                        response_data['method'],
+                                        response_data['status_code'])
+
+    print('JavaScript examples validated.')