Adding experimental branch buildflow

(cherry picked from commit c2b0276a60f1d21d18cc56d234f5dce0c5d1fffc)

.github/workflows/build.yml

@@ -1,9 +1,13 @@
 name: docker-buildx
 on:
   pull_request:
-    branches: master
+    branches:
+      - master
+      - experimental
   push:
-    branches: master
+    branches:
+      - master
+      - experimental
     tags:
       - '*.*'
 
@@ -112,15 +116,25 @@ jobs:
           password: ${{ secrets.REGISTRY_PASSWORD }}
       -
         name: Test build on Pull request
-        if: ${{ startsWith(steps.vars.outputs.type , 'head') &&  github.event.issue.pull_request }}
+        if: ${{ startsWith(steps.vars.outputs.type , 'head') &&  github.event.issue.pull_request && github.ref == 'refs/heads/master' }}
         uses: docker/build-push-action@v2
         with:
           context: .
           file: docker/${{ matrix.container }}/Dockerfile.build
           platforms: linux/amd64,linux/arm64,linux/arm/v7
+      -
+        name: Build experimental
+        if: ${{ github.ref == 'refs/heads/experimental' }}
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: docker/${{ matrix.container }}/Dockerfile.build
+          platforms: linux/amd64,linux/arm64,linux/arm/v7
+          push: true
+          tags: bpatrik/pigallery2:experimental-${{ matrix.container }}
       -
         name: Build and push nightly on new master commit
-        if: ${{ startsWith(steps.vars.outputs.type , 'head') &&  !github.event.issue.pull_request }}
+        if: ${{ startsWith(steps.vars.outputs.type , 'head') &&  !github.event.issue.pull_request && github.ref == 'refs/heads/master' }}
         uses: docker/build-push-action@v2
         with:
           context: .
@@ -130,7 +144,7 @@ jobs:
           tags: bpatrik/pigallery2:nightly-${{ matrix.container }}
       -
         name: Build and push release on new Tag
-        if: ${{ startsWith(steps.vars.outputs.type , 'tag') &&  !github.event.issue.pull_request }}
+        if: ${{ startsWith(steps.vars.outputs.type , 'tag') &&  !github.event.issue.pull_request && github.ref == 'refs/heads/master' }}
         uses: docker/build-push-action@v2
         with:
           context: .