fix: using pool_size as pg conn min_size if not set

Author: elvizlai

src/pgmq/queue.py

@@ -37,6 +37,7 @@ def __post_init__(self) -> None:
         user={self.username}
         password={self.password}
         """
+        self.kwargs.setdefault("min_size", self.pool_size)
         self.pool = ConnectionPool(conninfo, open=True, **self.kwargs)
         self._initialize_logging()
         if self.init_extension: