[WIP] Try to reduce image size

.github/workflows/deployment.yml

@@ -71,10 +71,50 @@ jobs:
           key: ${{ runner.os }}-gradle-${{ hashFiles('gradle/wrapper/gradle-wrapper.properties') }}
       - name: Build runtime image
         run: ./gradlew -PprojVersion="${{ steps.gitversion.outputs.AssemblySemVer }}" -PprojVersionInfo="${{ steps.gitversion.outputs.InformationalVersion }}" jlinkZip
+      - name: Debug state after build
+        run: |
+          find build -name "JabRef*.jar"
+        shell: bash
       - name: Build installer
         run: ./gradlew -PprojVersion="${{ steps.gitversion.outputs.AssemblySemVer }}" -PprojVersionInfo="${{ steps.gitversion.outputs.InformationalVersion }}" jpackage
         shell: bash
-      - name: Package application image
+      - name: Save portable jar, fix and output filename of portable jar
+        id: portablejar
+        if: matrix.displayName == 'linux'
+        run: |
+          mv build/distribution/JabRef/lib/app/mods/JabRef.merged*.jar JabRef-${{ steps.gitversion.outputs.Major }}.${{ steps.gitversion.outputs.Minor }}.jar
+          echo "::set-output name=file::$(ls JabRef*.jar)"
+        shell: bash
+      - name: Upload portable jar
+        if: matrix.displayName == 'linux'
+        uses: actions/upload-artifact@master
+        with:
+          name: JabRef-jar
+          path: ${{ steps.portablejar.outputs.file }}
+      # In case the timestamp of a file changes, the tar archive changes, because tar also stores file meta such as the file name and the file creation date.
+      # Therefore, the gzip file changes.
+      # Therefore, data needs to be synced by rsync.
+      # To prevent that, we set the timestamp to something "OKish" (not confiusing users that hard)
+      # We use "last monday", 00:00 as time stamp
+      - name: Determine timestamp for build
+        id: timestampforbuild
+        run: |
+          from datetime import datetime
+          from datetime import date
+          from datetime import timedelta
+          lastmonday = date.today().toordinal()
+          lastmonday = lastmonday - (lastmonday % 7) + 1
+          timestamp = datetime.fromordinal(lastmonday).strftime("%y%m%d")
+          print("::set-output name=timestamp::" + timestamp)
+        shell: python
+      - name: Post-process build
+        # Remove obsolete jar, update timestamps
+        run: |
+          find build -name "JabRef*.jar"
+          find build -name "JabRef*.jar" | xargs rm
+          find build -type f -exec touch -t ${{ steps.timestampforbuild.outputs.timestamp }}0000 {} \;
+        shell: bash
+     - name: Package application image
         run: ${{ matrix.archivePortable }}
         shell: bash
       - name: Rename files
@@ -119,6 +159,11 @@ jobs:
         with:
           name: JabRef-macOS
           path: build/distribution/
+      - name: Get portable JAR
+        uses: actions/download-artifact@master
+        with:
+          name: JabRef-jar
+          path: build/distribution/
       - name: Deploy to builds.jabref.org
         id: deploy
         uses: Pendect/action-rsyncer@v1.1.0