Refactor grpc-balancer to use Gunicorn and update playbook.yml for deployment

- Replaced the SSL server implementation in grpc-balancer.py with Gunicorn for improved performance and scalability.
- Updated playbook.yml to use Gunicorn for starting the grpc-balancer service, including SSL certificate configuration.
- Removed the waitress dependency in favor of Gunicorn, streamlining the application setup.

playbook.yml

@@ -200,7 +200,7 @@
           - grist-api
           - flask
           - requests
-          - waitress
+          - gunicorn
         extra_args: --break-system-packages
 
     - name: Create SSL certificate for grpcbalancer
@@ -229,7 +229,7 @@
           Type=simple
           User=root
           WorkingDirectory={{ ansible_env.HOME }}/node
-          ExecStart=/usr/bin/python3 {{ ansible_env.HOME }}/node/grpc-balancer.py
+          ExecStart=/usr/local/bin/gunicorn --certfile=/root/node/cert.pem --keyfile=/root/node/key.pem -b 0.0.0.0:5000 grpc-balancer:app
           Restart=always
           RestartSec=2