Build container images on Github Actions and push to multiple registries (#26247)

Modifications:
- Modify the workflow to build container images without pushing when the workflow file itself is modified
- Strip the leading ghcr.io/spack/ from env.container env.versioned to prepare pushing to multiple registries
- Fixed CentOS 7 and Amazon Linux builds
- Login and push to Docker Hub as well as Github Action
- Add a badge to README.md with the status of docker images

.github/workflows/build-containers.yml

@@ -1,8 +1,16 @@
-name: Build & Deploy Docker Containers
+name: Containers
 on:
+  # This Workflow can be triggered manually
+  workflow_dispatch:
   # Build new Spack develop containers nightly.
   schedule:
     - cron: '34 0 * * *'
+  # Run on pull requests that modify this file
+  pull_request:
+    branches:
+      - develop
+    paths:
+      - '.github/workflows/build-containers.yml'
   # Let's also build & tag Spack containers on releases.
   release:
     types: [published]
@@ -29,7 +37,7 @@ jobs:
 
       - name: Set Container Tag Normal (Nightly)
         run: |
-          container="ghcr.io/spack/${{ matrix.dockerfile[0]}}:latest"
+          container="${{ matrix.dockerfile[0] }}:latest"
           echo "container=${container}" >> $GITHUB_ENV
           echo "versioned=${container}" >> $GITHUB_ENV
 
@@ -37,7 +45,7 @@ jobs:
       - name: Set Container Tag on Release
         if: github.event_name == 'release'
         run: |
-          versioned="ghcr.io/spack/${{matrix.dockerfile[0]}}:${GITHUB_REF##*/}"
+          versioned="${{matrix.dockerfile[0]}}:${GITHUB_REF##*/}"
           echo "versioned=${versioned}" >> $GITHUB_ENV
 
       - name: Check ${{ matrix.dockerfile[1] }} Exists
@@ -48,6 +56,12 @@ jobs:
               exit 1;
           fi
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
       - name: Log in to GitHub Container Registry
         uses: docker/login-action@v1
         with:
@@ -55,18 +69,20 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v1
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v1
+      - name: Log in to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       - name: Build & Deploy ${{ matrix.dockerfile[1] }}
         uses: docker/build-push-action@v2
         with:
           file: share/spack/docker/${{matrix.dockerfile[1]}}
           platforms: ${{ matrix.dockerfile[2] }}
-          push: true
+          push: ${{ github.event_name != 'pull_request' }}
           tags: |
-            ${{ env.container }}
-            ${{ env.versioned }}
+            spack/${{ env.container }}
+            spack/${{ env.versioned }}
+            ghcr.io/spack/${{ env.container }}
+            ghcr.io/spack/${{ env.versioned }}