refactor: move bot tokens to .env, remove hardcoded credentials

- Remove IS_PROD flag and hardcoded tokens from config.py
- Read TELEGRAM_BOT_TOKEN and ADMINPANEL_TELEGRAM_BOT_TOKEN from env
- Add env_file: .env to lichess-bot and admin-bot in docker-compose.yml
- Add .env to .gitignore (no longer tracked)
- Add .env.example with test tokens

docker-compose.yml

@@ -24,6 +24,8 @@ services:
     volumes:
       - ./LichessClientTG_bot/data:/app/data
       - ./LichessClientTG_bot:/app
+    env_file:
+      - .env
     environment:
       - PYTHONPATH=/app
       - PYTHONUNBUFFERED=1
@@ -47,6 +49,8 @@ services:
     volumes:
       - ./LichessClientTG_bot/data:/app/data
       - ./LichessClientTG_bot:/app
+    env_file:
+      - .env
     environment:
       - PYTHONPATH=/app
       - PYTHONUNBUFFERED=1