Merge branch '21.2-EGAM7-AddCells-20201214' into '21.2'

add cell container to EGAM7

See merge request atlas/athena!39174

PhysicsAnalysis/DerivationFramework/DerivationFrameworkEGamma/share/EGAM7.py

@@ -390,3 +390,9 @@ EGAM7SlimmingHelper.ExtraVariables += PhotonsCPDetailedContent
 
 # This line must come after we have finished configuring EGAM7SlimmingHelper
 EGAM7SlimmingHelper.AppendContentToStream(EGAM7Stream)
+
+#Add full CellContainer
+EGAM7Stream.AddItem("CaloCellContainer#AODCellContainer")
+EGAM7Stream.AddItem("CaloClusterCellLinkContainer#egammaClusters_links")
+
+