✨ [#4908] Add docker compose flask app

Required for simulating a receiving service

docker/docker-compose.json-registration.yml

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+version: '3.8'
+
+name: json-registration
+
+services:
+  flask_app:
+    build: ./json-registration
+    ports:
+      - "80:80"
+    volumes:
+      - ./json-registration/:/app/
+
+networks:
+  open-forms-dev:
+    name: open-forms-dev

docker/json-registration/Dockerfile

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+# Use the official Python image from the Docker Hub
+FROM python:3.12-slim
+
+# Set the working directory
+WORKDIR /app
+
+# Copy the current directory contents into the container at /app
+COPY . /app
+
+# Install the dependencies
+RUN pip install Flask
+
+# Make port 80 available to the world outside this container
+EXPOSE 80
+
+# Run app.py when the container launches
+CMD ["python", "app.py"]

docker/json-registration/README.md

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+# JSON registration plugin
+
+The `docker-compose.json-registration.yml` compose file is available to run a mock service intended
+to simulate a receiving server to test the JSON registration backend plugin. It contains an endpoint for
+sending json data (`json_plugin`) and testing the connection (`test_connection`).
+
+The `json_plugin` endpoint returns a confirmation message that the data was received, together with the
+received data. The `test_connection` endpoint just returns an 'OK' message.
+
+## docker compose
+
+Start an instance in your local environment from the project root:
+
+```bash
+docker compose -f docker/docker-compose.json-registration.yml up -d
+```
+
+This starts a flask application at http://localhost:80/ with the endpoints `json_plugin` and `test_connection`.

docker/json-registration/app.py

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+from flask import Flask, jsonify, request
+
+
+app = Flask(__name__)
+
+@app.route("/json_plugin", methods=["POST"])
+def json_plugin_post():
+    data = request.get_json()
+
+    message = "No data" if data is None else "Data received"
+    return jsonify({"message": message, "data": data}), 201
+
+
+@app.route("/test_connection", methods=["GET"])
+def test_connection():
+    return jsonify({"message": "OK"}), 200
+
+
+if __name__ == "__main__":
+    app.run(host="0.0.0.0", port=80, debug=True)