feat: Add Booklooker client configuration and exception handling

- Introduced BooklookerConfig class for runtime configuration management.
- Created custom exceptions for API errors, including authentication and validation errors.
- Generated API contracts from OpenAPI specification, including endpoints and security schemes.
- Implemented models for articles, orders, and webhooks to facilitate data handling.
- Developed a webhook helper for processing and enriching webhook events.
- Added tests for configuration defaults, token expiration, and webhook enrichment.

examples/sync_usage.py

@@ -0,0 +1,14 @@
+from __future__ import annotations
+
+import os
+
+from booklooker_client import BooklookerConfig, SyncBooklookerClient
+
+
+api_key = os.environ.get("BOOKLOOKER_API_KEY", "REPLACE_ME")
+config = BooklookerConfig(api_key=api_key)
+
+with SyncBooklookerClient(config) as client:
+    token = client.authenticate()
+    print("Token acquired:", token.token)
+    print("Available endpoints:", client.available_endpoints)