Add explicit CellLink SG Key in configuration, ATLASRECTS-4821

Should fix ATLASRECTS-4821

2:23:01 StoreGateSvc_Impl                                 WARNING  setupProxy:: error setting up proxy for key EgammaDummyCellLink and clid 1134620868
12:23:01  Pre-existing valid DataProxy @0x111067840 found in Store for key EgammaDummyCellLink with clid 1134620868
12:23:01 ClassIDSvc                                           INFO  getRegistryEntries: read 31 CLIDRegistry entries for module ALL
12:23:01 StoreGateSvc_Impl                                 WARNING record_impl: Problem setting up the proxy for object @0x111511a80
12:23:01  recorded with key EgammaDummyCellLink of type CaloClusterCellLinkContainer (CLID 1134620868) in DataObject @0x111310760
12:23:01 VarHandle(StoreGateSvc+EgammaDummyCellLink[1134...  ERROR FILE:LINE (StatusCode SG::VarHandleBase::record_impl(std::unique_ptr<DataObject>, void*, bool, bool)): code 0: recordObject failed

PhysicsAnalysis/PrimaryDPDMaker/share/PerfDPD_EGamma.py

@@ -147,8 +147,9 @@ from DerivationFrameworkCalo.DerivationFrameworkCaloConf import DerivationFramew
 DESDM_EGAMMACellsInConeThinningEl = DerivationFramework__CellsInConeThinning( name = "DESDM_EGAMMACellsInConeThinningEl",
                                                                                InputSGKey = "Electrons",
                                                                                InputCellsSGKey = "AllCalo",
-                                                                               OutputClusterSGKey = "EgammaDummyClustersEl",                                                                            
-                                                                               deltaR = 0.5                                                            
+                                                                               OutputClusterSGKey ="EgammaDummyClustersEl",
+                                                                               OutputCellLinksSGKey="EgammaDummyClustersEl_links",
+                                                                               deltaR = 0.5
                                                                                )
 
 ToolSvc += DESDM_EGAMMACellsInConeThinningEl
@@ -156,7 +157,8 @@ ToolSvc += DESDM_EGAMMACellsInConeThinningEl
 DESDM_EGAMMACellsInConeThinningPh = DerivationFramework__CellsInConeThinning( name = "DESDM_EGAMMACellsInConeThinningPh", 
                                                                               InputSGKey = "Photons",
                                                                               InputCellsSGKey = "AllCalo",
-                                                                              OutputClusterSGKey = "EgammaDummyClustersPh",                                                                            
+                                                                              OutputClusterSGKey = "EgammaDummyClustersPh",
+                                                                              OutputCellLinksSGKey="EgammaDummyClustersPh_links",
                                                                               deltaR = 0.5                                                            
                                                                               )