#8600 add release notes

doc/release-notes/8600-duplicate-templates.md

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+###Duplicate Templates in Database
+Prior to this release making a copy of a Dataset Template was creating two copies, one of which is visible in the dataverse, the other not being assigned 
+a dataverse was invisible to the user (https://github.com/IQSS/dataverse/issues/8600). This release fixes the issue. 
+
+If you would like to remove these orphan templates you may run the follwing script:
+
+https://github.com/IQSS/dataverse/raw/develop/scripts/issues/8600/delete_orphan_templates_8600.sh
+
+In order to support the script two admin APIs for finding and deleting templates have been added.