Move cluster controller/agent main.zeek scripts into their own modules

This has no practical relevance other than allowing the two to be loaded a the
same time, which some of our (cluster-unrelated) tests require. Absence of
namespacing would trigger symbol clashes at this point.

scripts/policy/frameworks/cluster/agent/main.zeek

@@ -6,6 +6,8 @@
 
 @load ./api
 
+module ClusterAgent::Runtime;
+
 redef ClusterController::role = ClusterController::Types::AGENT;
 
 # The global configuration as passed to us by the controller

scripts/policy/frameworks/cluster/controller/main.zeek

@@ -8,6 +8,8 @@
 @load ./request
 @load ./util
 
+module ClusterController::Runtime;
+
 redef ClusterController::role = ClusterController::Types::CONTROLLER;
 
 global check_instances_ready: function(insts: set[string], tc: TableChange, inst: string);