added Github action support for "workflow_dispatch"

Added this in order to ensure that this Github action could be run manually, if needed, per https://github.blog/changelog/2020-07-06-github-actions-manual-triggers-with-workflow_dispatch/

.github/workflows/nightly-nuget.yml

@@ -3,6 +3,12 @@ on:
   schedule:
     # Once a day at 8 AM
    - cron: 0 8 * * *
+  workflow_dispatch:
+    inputs:
+      reason:
+        description: 'Reason'     
+        required: true
+        default: 'local testing'
 jobs:
   build-and-publish:
     runs-on: windows-latest
@@ -18,4 +24,4 @@ jobs:
     - name: Build Packages
       run: build.cmd nugetprerelease=dev
     - name: Push Packages
-      run: dotnet nuget push bin/nuget/*.nupkg
+      run: dotnet nuget push bin/nuget/*.nupkg