Make it possible to control which cluster node is in charge of running schedulers from dynamic input

Currently, in a cluster, the workaround for XWIKI-6235 is that only one node is in charge of running scheduled jobs. Problem is that the current way to do that (disabling the plugin in other nodes) does not fit a use case where you need all nodes images to be identical.

The minimum would be to control if the scheduler is enabled/disable, a variation of it which might allow for more features is to be able to indicate the id of the node in charge of running scheduled jobs.