ci: Emit to slack on merge to releases/* branch (#6318)

* Initial draft of Slack notification on releases/* merges

Test

* Add back proper Slack message content

* Feedback revisions

* Update .github/workflows/notify-slack-on-release-merge.yml
Co-authored-by: Zach Pomerantz <zzmp@uniswap.org>

* Update .github/workflows/notify-slack-on-release-merge.yml
Co-authored-by: Zach Pomerantz <zzmp@uniswap.org>

* Update .github/workflows/notify-slack-on-release-merge.yml
Co-authored-by: Zach Pomerantz <zzmp@uniswap.org>

* Comments

* revert to github env

* Add PR target back

* Revert multi-line

* write to context, add multi-line back

* Try other reference to context

* one other way of settings output...

* Pull from output

* Remove env

* Remove PR target

---------
Co-authored-by: Zach Pomerantz <zzmp@uniswap.org>

.github/workflows/notify-slack-on-release-merge.yml

+name: Slack notifications for releases/* merges
+
+# This CI job will push notifications to Slack whenever code is merged into any releases/* branch
+#
+# The steps of the command line kung-fu shown below are as follows:
+# First we take the JSON-formatted Github context
+#  echo $GITHUB_CONTEXT \
+# Then we parse out the specific fields we want for our messages using jq and format it into tab-separated values
+#  | jq '.event.commits[] | [.url, .id[0:7], .author.username, .timestamp, .message] | @tsv' \
+# We need to do some cleaning on this output - specifically removing quotes and replacing newlines with something easier to split
+#  | sed 's/"//g' | sed 's/\\t/;/g' | sed 's/\\n/;/g' | sed 's/\\//g' \
+# We then use awk to format the TSV into a Slack message
+#  | awk -F';' '{print "• <"$1"|"$2"> (<https://github.com/"$3"|"$3">, "$4") - "$5}' \
+# Finally, we need to deal with some escaping issues with newlines so that we don't break the Slack message format
+#  | sed 's/$/\\n/g' | tr -d '\n' \
+# Then shove the bytes into a file to store them in their exact format
+#  > /tmp/parsed_github_context
+
+on:
+  push:
+    branches:
+      - 'releases/*'
+
+jobs:
+  notify-slack:
+    name: 'Emit Slack notification(s)'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Parse event to slug
+        id: parse-slug
+        env:
+          GITHUB_CONTEXT: ${{ toJson(github) }}
+        # Formats the contents of the GitHub event into slugs: one line per commit, formatted for Slack.
+        # Explanation for each line is in the comments above.
+        run: |
+          echo $GITHUB_CONTEXT \
+          | jq '.event.commits[] | [.url, .id[0:7], .author.username, .timestamp, .message] | @tsv' \
+          | sed 's/"//g' | sed 's/\\t/;/g' | sed 's/\\n/;/g' | sed 's/\\//g' \
+          | awk -F';' '{print "• <"$1"|"$2"> (<https://github.com/"$3"|"$3">, "$4") - "$5}' \
+          | sed 's/$/\\n/g' | tr -d '\n' \
+          > /tmp/parsed_github_context
+          echo "SLACK_COMMITS=$(cat /tmp/parsed_github_context)" >> "$GITHUB_OUTPUT"
+      - name: Send custom JSON data to Slack workflow
+        id: slack
+        uses: slackapi/slack-github-action@007b2c3c751a190b6f0f040e47ed024deaa72844
+        with:
+          payload: |
+            {
+              "text": "GitHub Action build result: ${{ job.status }}\n${{ github.event.pull_request.html_url || github.event.head_commit.url }}",
+              "blocks": [
+                {
+                    "type": "divider"
+                },
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "*Code merged to <https://github.com/Uniswap/interface/tree/${{ github.ref }}|${{ github.ref_name }}> branch:*\n"
+                  }
+                },
+                {
+                    "type": "divider"
+                },
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "*Actor*: <https://github.com/${{ github.triggering_actor }}/|${{ github.triggering_actor }}>\n*Force pushed*: ${{ github.event.forced || false }}\n"
+                  }
+                },
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "${{ steps.parse-slug.outputs.SLACK_COMMITS || 'New branch created' }}"
+                  }
+                },
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "<${{ github.event.compare}}|View Diff>"
+                  }
+                }
+              ]
+            }
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+          SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK