text: Title: Keep pool connections count not less than min_size
  Body: Is there a way to specify min_size of the pool, so that even in case if connection isn't used longer than `max_inactive_connection_lifetime` it won't be closed if pool has exatly min_size connections oppened? 
  
  From what I see in the code, there is no such possibility at the moment and it may be tricky to add.
  
  We have trafik spikes and overall requests variation during the day, i.e. there is more requests in the evening than in the morning, and there is significant variation in number of requests hourly.
  So, we want to always have min_size of connections openned, but at the same time, we don't won't to keep all openned conections active all the time.
  