Make sure that when the rest proxy configuration gets changed, the channel manager tries to reconnect directly

Currently, in org.onehippo.cms7.channelmanager.restproxy.RestProxyServicesManager, there is logic for a reCheckIntervalMilliSeconds when a rest service is not available. As a result, it can grow to at most 5 minutes before a rest service is checked again. This is very inconvenient when you change the rest proxy configuration because then, you want the recheck to be done directly (otherwise you still think the configuration is broken, but you just have to wait 5 minutes)

Marked as high, because a broken channel mngr is always complex to fix, and this makes it quite a bit harder