.github/workflows: Publish the Ubuntu images at quay.io/toolbx/...

Until now, the Ubuntu images (versions 16.04, 18.04, 20.04, 22.04 and
22.10) were published at quay.io/toolbx-images/ubuntu-toolbox:22.04,
etc..  This changes the location to quay.io/toolbx/ubuntu-toolbox:22.04
and builds an image for Ubuntu 23.04 that was added recently [1].

Build and push when there are changes in the `images/ubuntu` directory
or in the GitHub workflow itself, as well as every other week (7th and
21st days of a month to be precise).

The toolbox(1) code and the system tests will be switched to the new
location after the first round of images are available.

[1] Commit 3cfb6bf888
    https://github.com/containers/toolbox/pull/1292

https://github.com/containers/toolbox/pull/483

Signed-off-by: Ievgen Popovych <jmennius@gmail.com>

.github/workflows/ubuntu-images.yaml

@@ -0,0 +1,61 @@
+name: "Images: Build and push Ubuntu toolbx images"
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - images/ubuntu/**
+      - .github/workflows/ubuntu-images.yaml
+  schedule:
+    - cron: '0 0 * * MON'
+
+# Prevent multiple workflow runs from racing
+concurrency: ${{ github.workflow }}
+
+env:
+  latest_release: '22.04'
+
+jobs:
+  build-and-push-images:
+    strategy:
+      matrix:
+        release: ['16.04', '18.04', '20.04', '22.04', '22.10', '23.04']
+
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Login to Quay.io
+        uses: docker/login-action@v2
+        with:
+          registry: quay.io
+          username: 'toolbx+github'
+          password: ${{ secrets.QUAY_ROBOT_TOKEN }}
+
+      - name: Build and push Ubuntu ${{ matrix.release }} toolbox image
+        uses: docker/build-push-action@v3
+        with:
+          context: images/ubuntu/${{ matrix.release }}
+          file: images/ubuntu/${{ matrix.release }}/Containerfile
+          platforms: linux/amd64,linux/arm64
+          push: true
+          no-cache: true
+          tags: quay.io/toolbx/ubuntu-toolbox:${{ matrix.release }}
+
+      - name: Push latest tag
+        if: env.latest_release == matrix.release
+        uses: docker/build-push-action@v3
+        with:
+          context: images/ubuntu/${{ matrix.release }}
+          file: images/ubuntu/${{ matrix.release }}/Containerfile
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: quay.io/toolbx/ubuntu-toolbox:latest