Description of problem

Currently, DNN Platform allows you to set a task to run on a named "list" of servers OR all servers. This creates a unique management issue and with the proposed changes in #5575 makes the management of set tasks harder.

Description of solution

The UI should be updated to only allow the specification of a SINGLE server name or not specified (all).

Description of alternatives considered

We could support multiple servers, however, looking at what is done, the key differentiation/feature is that you either run something everywhere. For example purge log. Or you have items that interact with the database and need to be executed once such as search scheduler.