Enhance Docker support and configuration

- Updated .env.example to recommend using docker.env and secrets for sensitive data.
- Modified .gitignore to include docker.env and secrets directory.
- Adjusted docker-compose.yml to utilize environment files and updated port mappings.
- Implemented read_env_or_file utility for better environment variable management.
- Refactored portfolio and trades routers to use the new utility for fetching environment variables.
- Added integration and phase 2 test updates for new environment variable handling.
- Created new documentation for Docker operations and secret management.
- Added placeholder files for Docker secrets and configuration.

config_utils.py

@@ -0,0 +1,15 @@
+from pathlib import Path
+import os
+from typing import Optional
+
+
+def read_env_or_file(name: str, default: Optional[str] = None) -> Optional[str]:
+    file_path = os.getenv(f"{name}_FILE")
+    if file_path:
+        return Path(file_path).read_text(encoding="utf-8").strip()
+
+    value = os.getenv(name)
+    if value is not None:
+        return value
+
+    return default