Added dockerimage-flashplugin.yml.

Added dockerimage-flashplugin.yml to build flashplugin-enabled PaleMoon on demand.

.github/workflows/dockerimage-flashplugin.yml

@@ -0,0 +1,27 @@
+name: _Manually_ build Docker image for Pale Moon browser with Flash plugin
+
+on:
+  repository_dispatch:
+    types: ['build-with-flashplugin']
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Build the Docker image
+        run: docker build . --file Dockerfile.flashplugin --tag vasilev/palemoon
+      - name: Log into registry
+        run: | 
+          echo "${{ secrets.DOCKERHUB_PASSWORD }}" | docker login -u ${{ secrets.DOCKERHUB_USERNAME }} --password-stdin
+      - name: Push image
+        run: |
+          # Strip git ref prefix from version
+          VERSION=$(echo "${{ github.ref }}" | sed -e 's,.*/\(.*\),\1,')
+          # Strip "v" prefix from tag name
+          [[ "${{ github.ref }}" == "refs/tags/"* ]] && VERSION=$(echo $VERSION | sed -e 's/^v//')
+          echo VERSION=$VERSION
+          docker tag vasilev/palemoon vasilev/palemoon:$VERSION-flashplugin
+          docker push vasilev/palemoon:$VERSION-flashplugin