a release note for the "zipper tool". (#6505)

doc/release-notes/6505-zipdownload-service.md

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+### A multi-file, zipped download optimization
+
+In this release we are offering an experimental optimization for the
+multi-file, download-as-zip functionality. If this option is enabled,
+instead of enforcing size limits, we attempt to serve all the files
+that the user requested (that they are authorized to download), but
+the request is redirected to a standalone zipper service running as a
+cgi executable. Thus moving these potentially long-running jobs
+completely outside the Application Server (Payara); and preventing
+service threads from becoming locked serving them. Since zipping is
+also a CPU-intensive task, it is possible to have this service running
+on a different host system, thus freeing the cycles on the main
+Application Server. (The system running the service needs to have
+access to the database as well as to the storage filesystem, and/or S3
+bucket).
+
+Please consult the scripts/zipdownload/README.md in the Dataverse 5
+source tree.
+
+The components of the standalone "zipper tool" can also be downloaded
+here:
+(my plan is to build the executable and to add it to the v5
+release files on github: - L.A.)
+https://github.com/IQSS/dataverse/releases/download/v5.0/zipper.zip.