feat: add workflow for creating release PRs with selected images

Author: Simen Andrè Vikestrand Skogum

.github/workflows/create-release-pr.yml

@@ -0,0 +1,67 @@
+name: Create Release PR (select images)
+
+on:
+  workflow_dispatch:
+    inputs:
+      dirs:
+        description: 'Comma-separated app dirs to promote (e.g. salamicontainers/salami/valkey/8,salamicontainers/salami/other/1)'
+        required: true
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  plan:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: dev
+          fetch-depth: 0
+
+      - name: Build release plan
+        id: plan
+        shell: bash
+        run: |
+          set -euo pipefail
+          IFS=, read -r -a ARR <<<"${{ github.event.inputs.dirs }}"
+          includes="[]"
+          for d in "${ARR[@]}"; do
+            d="${d//[$'\n\r\t ']/}"
+            [ -n "$d" ] || continue
+            if [ ! -f "$d/Dockerfile" ]; then
+              echo "Skip: $d (no Dockerfile)" >&2
+              continue
+            fi
+            if [ ! -f "$d/VERSION" ]; then
+              echo "Skip: $d (no VERSION)" >&2
+              continue
+            fi
+            ver="$(tr -d '\n\r\t ' < "$d/VERSION")"
+            major="$(basename "$d")"
+            app="$(basename "$(dirname "$d")")"
+            image="ghcr.io/${{ github.repository_owner }}/salami-${app}-${major}"
+            # Tags to publish on main: version and latest
+            tags="${image}:${ver},${image}:latest"
+            includes="$(jq -c --arg dir "$d" --arg img "$image" --arg ver "$ver" --arg tags "$tags" \
+              '. + [{dir:$dir,image:$img,version:$ver,tags:$tags}]' <<<"$includes")"
+          done
+          mkdir -p .github/releases
+          jq -c '{include: .}' <<<"$includes" > .github/releases/release-plan.json
+          echo "plan=$(cat .github/releases/release-plan.json)" >> "$GITHUB_OUTPUT"
+
+      - name: Create PR dev -> main with release plan
+        uses: peter-evans/create-pull-request@v6
+        with:
+          token: ${{ github.token }}
+          commit-message: "chore(release): promote selected images"
+          title: "Promote selected images to main"
+          body: |
+            This PR promotes the following images:
+            ```
+            ${{ steps.plan.outputs.plan }}
+            ```
+          branch: "promote/${{ github.run_id }}"
+          base: main
+          labels: promote