feat: Add comprehensive configuration system and examples

Added complete configuration support with multiple formats and examples
to help users easily configure py-wikijs for their projects.

New Features:
- Configuration file templates for ENV, YAML, JSON, and INI formats
- config_helper.py: Universal configuration loader and client factory
  * Auto-detects and loads configs from multiple formats
  * Supports environment variables, YAML, JSON, and INI files
  * Provides create_client_from_config() for easy client creation
  * Validates configuration and provides helpful error messages

Configuration Templates:
- config.env.example: Environment variables (Docker, 12-factor apps)
- config.yaml.example: YAML with multi-environment support
- config.json.example: JSON for programmatic configuration
- config.ini.example: INI for traditional setups

Usage Examples:
- using_env_config.py: Complete example using .env files
- using_yaml_config.py: Complete example using YAML configuration
- using_json_config.py: Complete example using JSON configuration

Documentation:
- docs/CONFIGURATION_GUIDE.md: Comprehensive configuration guide
  * All configuration methods explained
  * Security best practices
  * Environment-specific configurations
  * Troubleshooting guide

Benefits:
✅ Flexible configuration (choose your preferred format)
✅ Keep credentials secure (no hardcoding)
✅ Environment-specific configs (dev/staging/prod)
✅ Docker/container-ready
✅ Full validation and error handling
✅ Comprehensive documentation and examples

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/config.json.example

@@ -0,0 +1,51 @@
+{
+  "_comment": "py-wikijs JSON Configuration File",
+  "_usage": "Copy to config.json and update with your values",
+
+  "wikijs": {
+    "url": "https://wiki.example.com",
+    "auth": {
+      "method": "api_key",
+      "api_key": "your-api-key-here"
+    }
+  },
+
+  "client": {
+    "timeout": 30.0,
+    "rate_limit": 10.0,
+    "max_retries": 3,
+    "verify_ssl": true,
+    "pool_size": 10,
+    "user_agent": "MyApp/1.0 py-wikijs/0.1.0"
+  },
+
+  "logging": {
+    "debug": false,
+    "level": "INFO",
+    "format": "%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+    "file": {
+      "enabled": false,
+      "path": "/var/log/wikijs-client.log",
+      "max_bytes": 10485760,
+      "backup_count": 5
+    }
+  },
+
+  "metrics": {
+    "enabled": true,
+    "format": "prometheus"
+  },
+
+  "cache": {
+    "enabled": false,
+    "backend": "memory",
+    "ttl": 300,
+    "max_size": 1000
+  },
+
+  "features": {
+    "async_enabled": false,
+    "batch_enabled": true,
+    "auto_pagination": true
+  }
+}