Add example environment configuration and Docker Compose setup

- Introduced a new `.env.example` file to provide a template for environment variables used by the Scratchbox server.
- Added a `docker-compose.example.yml` file to facilitate easy deployment of the Scratchbox service with Docker.
- Updated `docker-entrypoint.sh` to enforce environment variable settings for server configuration.
- Removed the generation of a config key file from the workflow, simplifying the configuration process.
- Adjusted the README.md to reflect changes in configuration management and usage instructions.

docker-compose.example.yml

@@ -0,0 +1,10 @@
+services:
+  scratchbox:
+    image: git.s1d3sw1ped.com/s1d3sw1ped/scratchbox:latest
+    env_file:
+      - .env
+    ports:
+      - "8080:8080"
+    volumes:
+      - ./docker-data:/data
+    restart: unless-stopped