Load configuration file in app.config

mapping_provider/__init__.py

 """Initializes the FastAPI application."""
+import os
 
 from fastapi import FastAPI
 
+from mapping_provider import config
 from mapping_provider.api.common import router as version_router
 
 
@@ -11,5 +13,10 @@ def create_app() -> FastAPI:
         title="Mapping provider",
         description="Mapping provider endpoints for GÉANT maps",
     )
+
+    config_file = os.environ.get("CONFIG_FILE_NAME", "config.json")
+    with config_file.open() as f:
+        app.state.config = config.load(f)
+
     app.include_router(version_router)
     return app