Refactor: Use shared GitHub Action workflows

This change refactors the GitHub Actions workflows to use shared, reusable workflows from the `learningequality/.github` repository. This promotes consistency and maintainability across repositories.

The following changes were made:
- Created `.github/workflows/call-contributor-pr-reply.yml`
- Created `.github/workflows/call-holiday-message.yml`
- Renamed `.github/workflows/update-pr-spreadsheet.yml` to `.github/workflows/call-update-pr-spreadsheet.yml` and updated its content.

Author: google-labs-jules[bot]

.github/workflows/call-contributor-pr-reply.yml

@@ -0,0 +1,12 @@
+name: Send reply on a new contributor pull request
+on:
+  pull_request_target:
+    types: [opened]
+jobs:
+  call-workflow:
+    name: Call shared workflow
+    uses: learningequality/.github/.github/workflows/contributor-pr-reply.yml@main
+    secrets:
+      LE_BOT_APP_ID: ${{ secrets.LE_BOT_APP_ID }}
+      LE_BOT_PRIVATE_KEY: ${{ secrets.LE_BOT_PRIVATE_KEY }}
+      SLACK_COMMUNITY_NOTIFICATIONS_WEBHOOK_URL: ${{ secrets.SLACK_COMMUNITY_NOTIFICATIONS_WEBHOOK_URL }}

.github/workflows/call-holiday-message.yml

@@ -0,0 +1,14 @@
+name: Post holiday message on pull request or issue comment
+on:
+  pull_request_target:
+    types: [opened]
+  issue_comment:
+    types: [created]
+jobs:
+  call-workflow:
+    name: Call shared workflow
+    uses: learningequality/.github/.github/workflows/holiday-message.yml@main
+    secrets:
+      LE_BOT_APP_ID: ${{ secrets.LE_BOT_APP_ID }}
+      LE_BOT_PRIVATE_KEY: ${{ secrets.LE_BOT_PRIVATE_KEY }}
+      SLACK_COMMUNITY_NOTIFICATIONS_WEBHOOK_URL: ${{ secrets.SLACK_COMMUNITY_NOTIFICATIONS_WEBHOOK_URL }}

.github/workflows/update-pr-spreadsheet.yml renamed to .github/workflows/call-update-pr-spreadsheet.yml

@@ -1,12 +1,15 @@
 name: Update community pull requests spreadsheet
 on:
   pull_request_target:
-    types: [assigned,unassigned,opened,closed,reopened]
+    types: [assigned, unassigned, opened, closed, reopened, edited, review_requested, review_request_removed]
 
 jobs:
-  call-update-spreadsheet:
+  call-workflow:
+    name: Call shared workflow
     uses: learningequality/.github/.github/workflows/update-pr-spreadsheet.yml@main
     secrets:
+      LE_BOT_APP_ID: ${{ secrets.LE_BOT_APP_ID }}
+      LE_BOT_PRIVATE_KEY: ${{ secrets.LE_BOT_PRIVATE_KEY }}
       CONTRIBUTIONS_SPREADSHEET_ID: ${{ secrets.CONTRIBUTIONS_SPREADSHEET_ID }}
       CONTRIBUTIONS_SHEET_NAME: ${{ secrets.CONTRIBUTIONS_SHEET_NAME }}
       GH_UPLOADER_GCP_SA_CREDENTIALS: ${{ secrets.GH_UPLOADER_GCP_SA_CREDENTIALS }}