Migrate Proposal from Google Doc: Extra HTTP parameters in the blackbox exporter

| Document | Initial date | Status | Pull requests |
| -------- | ------------ | ------ | ------------- |
| [Extra HTTP parameters in the blackbox exporter](https://docs.google.com/document/d/1VwqXi2TOb5KXaZY6Iio7411x64pJao3GusX8MqYsJ2g/edit) | 2021‑06‑23 | Proposed | |