configurable trans-membrance hostcall blocklist

site/doc/pages/http_request_async.txt

@@ -0,0 +1,7 @@
+# http_request_async
+
+```cpp
+u64 http_request_async(DValue req)
+```
+
+Starts the same bounded curl-backed request as `http_request()` in the file-backed async job registry and returns a job id. Use `job_await()` or `job_result()` to retrieve the HTTP result.