[DSC-2451] decrease commit size on metadata import

(cherry picked from commit 80f3a08068d5a21decd247d779daa7a9bf33a74d)

Author: francescopioscognamiglio

dspace/config/modules/bulkedit.cfg

@@ -38,7 +38,7 @@ bulkedit.allow-bulk-deletion = dspace.agreements.end-user
 # After too much consecutive records everything starts to slow down because too many things are being loaded into memory
 # If we commit these to the database these are cleared out of our memory and we don't lose as much performance
 # By default this is set to 100
-bulkedit.change.commit.count = 100
+bulkedit.change.commit.count = 20
 
 ### Bulkedit Metadata export settings
 # The maximum amount of items that can be exported using the "metadata-export" / "metadata-export-search" script