docs: add Trivy scan badges

| Input / Variable | Description                              | Default value     |

| --------------------- | ---------------------------------------- | ----------------- |

| `image` / `HURL_IMAGE` | The Docker image used to run Hurl. | `ghcr.io/orange-opensource/hurl:latest` |

| `image` / `HURL_IMAGE` | The Docker image used to run Hurl. | `ghcr.io/orange-opensource/hurl:latest` <br/>[![Trivy Badge](https://to-be-continuous.gitlab.io/doc/secu/trivy-badge-HURL_IMAGE.svg)](https://to-be-continuous.gitlab.io/doc/secu/trivy-HURL_IMAGE) |

| `test-files` / `HURL_TEST_FILES` | The Hurl test files to run | `--glob **/*.hurl` |

| `extra-args` / `HURL_EXTRA_ARGS` | Hurl extra [run options](https://hurl.dev/docs/manual.html#options) | _none_ |

| `review-enabled` / `REVIEW_ENABLED` | Set to `true` to enable Hurl tests on review environments (dynamic environments instantiated on development branches) | _none_ (disabled) |