Automatically build overcloud host images

Trigger building new overcloud host images when a change to
pulp-repo-versions.yml is pushed to stackhpc/2025.1.

Author: MoteHue

.github/overcloud-host-image-build-path-filters.yml

@@ -0,0 +1,3 @@
+# This file is a list of path filters for the PR workflow in .github/workflows/stackhpc-pull-request.yml.
+pulp-repo-versions: &pulp-repo-versions
+  - 'etc/kayobe/pulp-repo-versions.yml'

.github/path-filters.yml renamed to .github/stackhpc-pull-request-path-filters.yml

@@ -34,7 +34,7 @@ jobs:
         id: changes
         with:
           # Filters are defined in this file.
-          filters: .github/path-filters.yml
+          filters: .github/stackhpc-pull-request-path-filters.yml
 
   tox:
     runs-on: ubuntu-24.04

.github/workflows/stackhpc-pull-request.yml

@@ -0,0 +1,45 @@
+---
+name: Trigger overcloud host image build
+on:
+  push:
+    branches:
+      - automatically-build-overcloud-host-images
+      # - stackhpc/2025.1
+
+jobs:
+  check-changes:
+    runs-on: ubuntu-24.04
+    name: Check changed files
+    if: github.repository == 'stackhpc/stackhpc-kayobe-config'
+    outputs:
+      pulp-repo-versions: ${{ steps.changes.outputs.pulp-repo-versions }}
+    steps:
+      - name: GitHub Checkout
+        uses: actions/checkout@v4
+
+      - name: Check changed files
+        uses: dorny/paths-filter@v3
+        id: changes
+        with:
+          filters: .github/overcloud-host-image-build-path-filters.yml
+
+  trigger-overcloud-host-image-build:
+    runs-on: ubuntu-24.04
+    name: Trigger overcloud host image build
+    needs:
+      - check-changes
+    if: ${{ needs.check-changes.outputs.pulp-repo-versions == 'true' }}
+    steps:
+      - name: Trigger overcloud host image build
+        run: |
+          gh workflow run \
+          overcloud-host-image-build.yml \
+          --repo stackhpc/stackhpc-kayobe-config \
+          --ref $BRANCH_NAME
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BRANCH_NAME: ${{ github.head_ref || github.ref_name }}
+
+      - name: Display link to overcloud host image build workflows
+        run: |
+          echo "::notice Overcloud host image build workflows: https://github.com/stackhpc/stackhpc-kayobe-config/actions/workflows/overcloud-host-image-build.yml"