Update Compress Images GitHub Actions workflow (#4478)

The Compress Images workflow isn't catching most of the images being
committed. This is, in part, because it doesn't run with permissions to
edit PRs on forks.  This updates the configuration to open a new PR when
a commit is merged, if there are images that can be compressed. It also
adds a scheduled run, in case something gets missed.
Based on https://github.com/calibreapp/image-actions#combined-workflow

.github/workflows/image-actions.yml

@@ -1,14 +1,42 @@
 name: Compress images
-on: pull_request
+on:
+  pull_request: # PRs with image (but we can't push changes back to other forks)
+    paths:
+      - "**.jpg"
+      - "**.jpeg"
+      - "**.png"
+      - "**.webp"
+  push:
+    branches:
+      - development # merging PRs from other forks (will open a new PR)
+  worflow_dispatch: # on demand
+  schedule:
+    - cron: "0 0 * * 0" # every Sunday at midnight
 jobs:
   build:
+    if: | # Only run on main repo on and PRs that match the main repo.
+      github.repository == 'dnnsoftware/Dnn.Platform' &&
+      (github.event_name != 'pull_request' ||
+       github.event.pull_request.head.repo.full_name == github.repository)
     name: calibreapp/image-actions
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repo
         uses: actions/checkout@v2
 
       - name: Compress Images
+        id: compress_images
         uses: calibreapp/[email protected]
         with:
           githubToken: ${{ secrets.GITHUB_TOKEN }}
+          compressOnly: ${{ github.event_name != 'pull_request' }} # For non-Pull Requests, run in compressOnly mode and we'll PR after.
+
+      - name: Create Pull Request
+        if: | # If it's not a Pull Request then commit any changes as a new PR.
+          github.event_name != 'pull_request' && steps.compress_images.outputs.markdown != ''
+        uses: peter-evans/create-pull-request@v3
+        with:
+          title: Auto Compress Images
+          branch-suffix: timestamp
+          commit-message: Compress Images
+          body: ${{ steps.compress_images.outputs.markdown }}