Setup make index for testing (#1183)

- Reconfigure index file generation
- checkout gh-pages branch in promote.yaml
- fix helm-index make target
- add gh-pages folder in .gitignore

Signed-off-by: Miles Wilson <wilson.mil@icloud.com>
Co-authored-by: Hao Liu <haoli@redhat.com>
Co-authored-by: Christian Adams <rooftopcellist@gmail.com>

.github/workflows/promote.yaml

@@ -8,7 +8,14 @@ jobs:
   promote:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
+        with:
+          depth: 0
+
+      - uses: actions/checkout@v3
+        with:
+          ref: gh-pages
+          path: gh-pages
 
       - name: Log in to GHCR
         run: |