fix: ensure /opt/detector/setup.sh points to epic

Not a solution (to the problem that default isn't taking effect), but probably a workaround.

detectors.yaml

 detectors:
-  athena:
+  epic:
     nightly:
-      version: master
+      default: true
+      version: main
       ip:
         config: ip6
         version: master
-  ecce:
+  athena:
     nightly:
-      version: main
+      version: master
       ip:
         config: ip6
         version: master
-  epic:
+  ecce:
     nightly:
-      default: true
       version: main
       ip:
         config: ip6