ft: workflow to post release notes to slack

.github/workflows/post-to-slack.yaml

@@ -0,0 +1,67 @@
+name: 'Post messages to Slack'
+
+# Must use secrets: inherit
+
+# Check that your service repo is private if this service-framework repo is also private
+# Sample concurrency config:
+# concurrency:
+#   group: ci-workflow-${{ github.ref }}-${{ github.event_name }}
+#   cancel-in-progress: true
+
+on:
+  workflow_call:
+    inputs:
+      channel_id:
+        description: 'Channel ID where the release notes will be posted'
+        type: string
+        required: true
+      title:
+        description: 'Title of the message'
+        type: string
+        required: true
+      body:
+        description: 'Body of the message'
+        type: string
+        required: true
+      runs-on:
+        description: 'Type of machine to run the job on'
+        type: string
+        default: ${{ github.event.repository.private && 'self-hosted' || 'ubuntu-latest' }}
+
+jobs:
+  prepare:
+    runs-on: ${{ inputs.runs-on }}
+    env:
+      title: ${{ inputs.title }}
+      body: ${{ inputs.body }}
+    steps:
+      - run: |
+        for env_var in title body; do
+          echo "$env_var=$(<<<"${!env_var}" sed -E '
+            s/^\* /• /                                              # bullet point
+            s/## (.+)/*\1*\n/                                       # heading
+            s/\*\*(.+?)\*\*/_\1_/g                                  # emphasis
+            s/&/\&amp;/g;s/</\&lt;/g;s/>/\&gt;/g                    # escape
+            s,https://.+?/(pull/[0-9]+|[^/ ]+\.\.\.[^/ ]+),<&|\1>,g # shorten GitHub links
+            1h;1!H;$!d;x;s/\n/\\n/g                                 # escape newlines')" >> "$GITHUB_ENV"
+        done
+  post_to_slack:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+      - uses: slackapi/slack-github-action@485a9d42d3a73031f12ec201c457e2162c45d02d # v2.0.0
+        with:
+          method: chat.postMessage
+          token: ${{ secrets.SLACK_BOT_TOKEN }}
+          payload: |
+            channel: ${{ inputs.channel_id }}
+            text: ${{ env.title }}
+            blocks:
+              - type: section
+                text:
+                  type: mrkdwn
+                  text: {{ env.title }}
+              - type: divider
+              - type: section
+                text:
+                  type: mrkdwn
+                  text: {{ env.body }}