Build all contributed recipes automatically (#1973)

* Build all contributed recipes automatically

* Add missing file

* Add checkout repo

* Fix matrix

* Remove unused var

* Add typing

docs/contributing/recipes.md

@@ -6,7 +6,7 @@ Follow the process below to add a new recipe:
 1. Open the `docs/using/recipes.md` source file.
 2. Add a second-level Markdown heading naming your recipe at the bottom of the file (e.g., `## Slideshows with JupyterLab and RISE`)
 3. Write the body of your recipe under the heading, including whatever command line, links, etc. you need.
-4. If you have a Dockerfile, please put it in a `recipe_code` subdirectory
-   and update [contributed-recipes workflow](https://github.com/jupyter/docker-stacks/blob/main/.github/workflows/contributed-recipes.yml) to include your file.
+4. If you have a Dockerfile, please put it in a `recipe_code` subdirectory.
+   This file will be built automatically by [contributed-recipes workflow](https://github.com/jupyter/docker-stacks/blob/main/.github/workflows/contributed-recipes.yml).
 5. [Submit a pull request](https://github.com/PointCloudLibrary/pcl/wiki/A-step-by-step-guide-on-preparing-and-submitting-a-pull-request) (PR) with your changes.
    Maintainers will respond and work with you to address any formatting or content issues.

docs/using/recipe_code/generate_matrix.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+# Copyright (c) Jupyter Development Team.
+# Distributed under the terms of the Modified BSD License.
+import json
+from pathlib import Path
+from typing import Any
+
+THIS_DIR = Path(__file__).parent.resolve()
+
+
+def generate_matrix() -> dict[str, Any]:
+    dockerfiles = sorted(file.name for file in THIS_DIR.glob("*.dockerfile"))
+    return {"dockerfile": dockerfiles}
+
+
+if __name__ == "__main__":
+    print("matrix=" + json.dumps(generate_matrix()))