chore: add caching for building gh-pages faster

Author: themightychris

.github/workflows/gh-pages.yml

@@ -10,6 +10,15 @@ jobs:
   gh-pages-projection:
     runs-on: ubuntu-latest
     steps:
+    - name: Initialize Chef Habitat artifacts cache directory
+      run: |
+        sudo mkdir -p /hab/cache/artifacts
+        sudo chown runner:docker -R /hab
+    - name: Cache Chef Habitat artifacts
+      uses: actions/cache@v1
+      with:
+        path: /hab/cache/artifacts
+        key: hab-cache-artifacts
     - name: 'Update holobranch: gh-pages'
       uses: JarvusInnovations/hologit@actions/projector/v1
       env: