Align golang types with openapi.yaml schema (#628)

Change Format constant from `file_path` to `filepath` to match the
OpenAPI schema definition.

This is not used by any servers yet, nor is it enforced by the database,
so it's safe to change.

scripts/test_publish.sh

@@ -102,7 +102,7 @@ cat > "$PAYLOAD_FILE" << EOF
           "type": "positional",
           "name": "config",
           "description": "Configuration file path",
-          "format": "file_path",
+          "format": "filepath",
           "isRequired": false,
           "default": "./config.json"
         }