Add ordering to Standalone Agents, Cluster Agents and Subagent Clusters

Current Situation

• When managing Subagents then users can manually specify a sort order by moving the Subagent.
• This feature is not available for Standalone Agents, for Cluster Agents and for Subagent Clusters.

Desired Behavior

• Similar to Subagents users should be able to move Standalone Agents, Cluster Agents and Subagent Clusters to an arbitrary sort order.
• This functionality affects the API that should introduce the sort order and the GUI that should offer the related operation.