[ClientSDKs/C#] Use gpr for Nuget github action

Author: mdashti

.github/workflows/nuget-pack.yml

@@ -36,11 +36,14 @@ jobs:
     - name: Add private GitHub registry to NuGet
       run: dotnet nuget add source https://nuget.pkg.github.com/RelationalAI-oss/index.json -n GPR -u RelationalAI-oss -p ${{ secrets.GITHUB_TOKEN }} --store-password-in-clear-text
 
+    - name: Install gpr tool
+      run: dotnet tool install gpr -g
+
     - name: Push generated package to GitHub registry
       run: |
         for f in DelveClientSDK/bin/Release/*.nupkg
         do
-          dotnet nuget push $f --source "GPR"
+          gpr push $f -k ${{ secrets.GITHUB_TOKEN }}
         done
       shell: bash