ci: Add Slack notifications when releases and pre-releases are cut (#9596)

Automatically notify the team when pre-releases and releases are cut.

[Pre-release notification rendered](https://app.slack.com/block-kit-builder/TREF53MTJ#%7B%22blocks%22:%5B%7B%22type%22:%22section%22,%22text%22:%7B%22type%22:%22mrkdwn%22,%22text%22:%22✨%20New%20Tendermint%20pre-release:%20%3Chttps://github.com/tendermint/tendermint/releases/tag/v0.37.0-rc1%7Cv0.37.0-rc1%3E%22%7D%7D%5D%7D)

[Release notification rendered](https://app.slack.com/block-kit-builder/TREF53MTJ#%7B%22blocks%22:%5B%7B%22type%22:%22section%22,%22text%22:%7B%22type%22:%22mrkdwn%22,%22text%22:%22🚀%20New%20Tendermint%20release:%20%3Chttps://github.com/tendermint/tendermint/releases/tag/v0.34.22%7Cv0.34.22%3E%22%7D%7D%5D%7D)

---

#### PR checklist

- [x] Tests written/updated, or no tests needed
- [x] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [x] Updated relevant documentation (`docs/`) and code comments, or no
      documentation updates needed

.github/workflows/pre-release.yml

@@ -8,7 +8,7 @@ on:
       - "v[0-9]+.[0-9]+.[0-9]+-rc[0-9]+"      # e.g. v0.37.0-rc1, v0.38.0-rc10
 
 jobs:
-  goreleaser:
+  prerelease:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -38,3 +38,28 @@ jobs:
           args: release --rm-dist --release-notes=../release_notes.md
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  prerelease-success:
+    needs: prerelease
+    if: ${{ success() }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Notify Slack upon pre-release
+        uses: slackapi/slack-github-action@v1.22.0
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+          SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK
+          RELEASE_URL: "${{ github.server_url }}/${{ github.repository }}/releases/tag/${{ github.ref_name }}"
+        with:
+          payload: |
+            {
+              "blocks": [
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": ":sparkles: New Tendermint pre-release: <${{ env.RELEASE_URL }}|${{ github.ref_name }}>"
+                  }
+                }
+              ]
+            }

.github/workflows/release.yml

@@ -6,7 +6,7 @@ on:
       - "v[0-9]+.[0-9]+.[0-9]+"  # Push events to matching v*, i.e. v1.0, v20.15.10
 
 jobs:
-  goreleaser:
+  release:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -35,3 +35,28 @@ jobs:
           args: release --rm-dist --release-notes=../release_notes.md
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  release-success:
+    needs: release
+    if: ${{ success() }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Notify Slack upon release
+        uses: slackapi/slack-github-action@v1.22.0
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+          SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK
+          RELEASE_URL: "${{ github.server_url }}/${{ github.repository }}/releases/tag/${{ github.ref_name }}"
+        with:
+          payload: |
+            {
+              "blocks": [
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": ":rocket: New Tendermint release: <${{ env.RELEASE_URL }}|${{ github.ref_name }}>"
+                  }
+                }
+              ]
+            }