Consider adding some hook for refreshing resource after idle timeout is reached

[elhigu]

Currently if min resources is > 0 and they are idle for a long time in the pool the resource might get stale without notification (at least postgresql does that in some cases).

This behaviour basically renders having minimum amount of connections in config useless, because having stale resources waiting in pool is not useful.

We could add one more hook to the config which will be called for resource when idle timeout is reached and resource cannot be destroyed and freed because of pool min config value.