ci: add changelogs to automated version updates

Add the links to the changelogs of the freshly updated components to the
automated PR that does the update. This allow verifying that we are not
missing any important changes before merging the update. This happened
recently with node-exporter 1.2 which changed some flag names that we
took 3 months to update.

Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>

.github/workflows/versions.yaml

@@ -23,11 +23,15 @@ jobs:
       with:
         go-version: 1.16
     - name: Upgrade versions
+      id: versions
       run: |
         export GITHUB_TOKEN=${{ secrets.GITHUB_TOKEN }}
         # Write to temporary file to make update atomic
         scripts/generate-versions.sh > /tmp/versions.json
         mv /tmp/versions.json jsonnet/kube-prometheus/versions.json
+        # Get the links to the changelogs of the updated versions and make them
+        # available to the reviewers
+        echo ::set-output name=new_changelogs::$(scripts/get-new-changelogs.sh)
       if: matrix.branch == 'main'
     - name: Update jsonnet dependencies
       run: |
@@ -49,7 +53,12 @@ jobs:
 
           This is an automated version and jsonnet dependencies update performed from CI.
 
-          Configuration of the workflow is located in `.github/workflows/versions.yaml`
+          Please review the following changelogs to make sure that we don't miss any important
+          changes before merging this PR.
+
+          ${{ steps.versions.outputs.new_changelogs }}
+
+          Configuration of the workflow is located in `.github/workflows/versions.yaml`.
 
           ## Type of change