fix: allow empty secrets section

secrets can also be defined per domain, no need for a global section

nyacme/config.py

@@ -86,8 +86,8 @@ T = TypeVar('T')
 
 def config_parse_dict(raw_conf: dict[str, Any], key: str, parse_item: Callable[[Any], T]) -> dict[str, T]:
     if key not in raw_conf:
-        log.error(f'missing "{key}" in config')
-        sys.exit(1)
+        log.warning(f'missing "{key}" in config')
+        return {}
 
     result: dict[str, T] = {}