ci: sync release to pg branch (#35888)

## Description
This CI job is responsible for syncing changes from the release branch
to the pg branch. This happens for every commit merged to release
branch, similar to `Sync Community Workflow`

Fixes #`Issue Number`  

## Automation

/ok-to-test tags="@tag.Sanity"

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/10571814611>
> Commit: 9bc44fc0cc762d52854da3b4e2f8c3e995909ccd
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=10571814611&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Sanity`
> Spec:
> <hr>Tue, 27 Aug 2024 05:00:52 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit


- **New Features**
- Introduced an automated workflow for merging changes from the release
branch to the pg branch, enhancing integration and development
efficiency.
- Added notifications for merge conflicts to improve communication and
resolution tracking.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.github/workflows/sync-release-to-pg.yml

@@ -0,0 +1,84 @@
+name: Merge release to pg
+
+on:
+  push:
+    branches:
+      - release  # Trigger on push to the release branch
+
+jobs:
+  merge-release-to-pg:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout release branch
+        uses: actions/checkout@v3
+        with:
+          ref: release  # Checkout the release branch
+
+      - name: Fetch all branches
+        run: git fetch --all
+
+      - name: Checkout pg branch
+        run: git checkout pg
+
+      - name: Get new commits from release
+        id: get_commits
+        run: |
+          COMMITS=$(git log pg..release --oneline | awk '{print $1}')
+          echo "COMMITS=\"$COMMITS\"" >> $GITHUB_ENV
+
+      - name: Merge commits one by one
+        id: merge_commits
+        run: |
+          # Initialize an empty list for conflicted commits
+          conflicted_commits=()
+
+          # Convert the string of commits to an array
+          IFS=' ' read -r -a commit_array <<< "$COMMITS"
+
+          # Loop through each commit
+          for commit in "${commit_array[@]}"; do
+            echo "Merging commit $commit"
+            git cherry-pick $commit || {
+              echo "Conflict detected with commit $commit"
+              conflicted_commits+=($commit)
+              git cherry-pick --abort
+            }
+          done
+
+          # Save conflicted commits to environment variable
+          echo "CONFLICTED_COMMITS=\"${conflicted_commits[@]}\"" >> $GITHUB_ENV
+
+      - name: Push changes
+        if: success() && steps.merge_commits.outputs.CONFLICTED_COMMITS == ''
+        run: |
+          git push origin pg
+
+      - name: Notify on merge conflicts
+        if: steps.merge_commits.outputs.CONFLICTED_COMMITS != ''
+        env:
+          REPOSITORY_URL: ${{ github.repositoryUrl }}
+        run: |
+          # Prepare the message for Slack
+          message="Merge conflict detected while merging release into pg branch. Conflicted commits:\n"
+          for commit in $CONFLICTED_COMMITS; do
+            commit_url="$REPOSITORY_URL/commit/$commit"
+            message+="$commit_url\n"
+          done
+
+          # Send the message to Slack
+          # This unwieldy horror of a sed command, converts standard Markdown links to Slack's unwieldy link syntax.
+          slack_message="$(echo "$message" | sed -E 's/\[([^]]+)\]\(([^)]+)\)/<\2|\1>/g')"
+
+          # This is the ChannelId of the proj postgres channel.
+          body="$(jq -nc \
+            --arg channel C06Q3A97USE \
+            --arg text "$slack_message" \
+            '$ARGS.named'
+          )"
+
+          curl --version
+          curl -v https://slack.com/api/chat.postMessage \
+            --header 'Authorization: Bearer ${{ secrets.SLACK_APPSMITH_ALERTS_TOKEN }}' \
+            --header 'Content-Type: application/json; charset=utf-8' \
+            --data-raw "$body"