Move prysm to unclog for changelog management (#14782)

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -33,5 +33,5 @@ Fixes #
 **Acknowledgements**
 
 - [ ] I have read [CONTRIBUTING.md](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md).
-- [ ] I have made an appropriate entry to [CHANGELOG.md](https://github.com/prysmaticlabs/prysm/blob/develop/CHANGELOG.md).
+- [ ] I have included a uniquely named [changelog fragment file](https://github.com/prysmaticlabs/prysm/blob/develop/CONTRIBUTING.md#maintaining-changelogmd).
 - [ ] I have added a description to this PR with sufficient context for reviewers to understand this PR.

.github/workflows/changelog.yml

@@ -1,33 +1,35 @@
-name: CI
+# This workflow will build a golang project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-go
+
+name: changelog
 
 on:
   pull_request:
-    branches:
-      - develop
+    branches: [ "develop" ]
 
 jobs:
-  changed_files:
-    runs-on: ubuntu-latest 
-    name: Check CHANGELOG.md
+  run-changelog-check:
+    runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - name: changelog modified
-        id: changelog-modified
+      - name: Checkout source code
+        uses: actions/checkout@v3
+
+      - name: Download unclog binary
+        uses: actions/download-artifact@v4
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          repository: OffchainLabs/unclog
+          name: unclog
+          run-id: 12679708867
+
+      - name: Get new changelog files
+        id: new-changelog-files
         uses: tj-actions/changed-files@v45
         with:
-          files: CHANGELOG.md
+          files: |
+            changelog/**.md
 
-      - name: List all changed files
+      - name: Run lint command
         env:
-          ALL_CHANGED_FILES: ${{ steps.changelog-modified.outputs.all_changed_files }}
-        run: |
-          if [[ ${ALL_CHANGED_FILES[*]} =~ (^|[[:space:]])"CHANGELOG.md"($|[[:space:]]) ]];
-          then
-            echo "CHANGELOG.md was modified.";
-            exit 0;
-          else
-            echo "CHANGELOG.md was not modified.";
-            echo "Please see CHANGELOG.md and follow the instructions to add your changes to that file."
-            echo "In some rare scenarios, a changelog entry is not required and this CI check can be ignored."
-            exit 1;
-          fi
+          ALL_ADDED_MARKDOWN: ${{ steps.new-changelog-files.outputs.added_files }}
+        run: chmod +x unclog && ./unclog check -fragment-env=ALL_ADDED_MARKDOWN