Add action to update PR description with netlify staging links (#3359)

## Pull Request Info - SDK Docs Consolidation

Jira ticket: [DOCSP-42152](https://jira.mongodb.org/browse/DOCSP-42152)

## Release Notes
- Adds a new GitHub Action that generates staging links and inserts them
into the PR description.

Author: MongoCaleb

.github/pull_request_template.md

@@ -2,9 +2,10 @@
 
 Jira ticket: https://jira.mongodb.org/browse/DOCSP-NNNNN
 
-*Staged Page*
-
-- [PAGE_NAME](https://docs-mongodbcom-staging.corp.mongodb.com/realm/docsworker-xlarge/BRANCH_NAME/)
+### Staging Links
+<!-- start insert-links -->
+-
+<!-- end insert-links -->
 
 *Page Source*
 

.github/workflows/netflify-preview-links.yml

@@ -0,0 +1,56 @@
+name: Add Netlify Links To Changed Pages
+on:
+    workflow_call:
+    pull_request_target:
+jobs:
+    get-pr-changes:
+        name: Get Changed Files & Update PR Description
+        runs-on: ubuntu-latest
+        permissions:
+            issues: write
+            contents: write
+            pull-requests: write
+            repository-projects: write
+        steps:
+          - uses: actions/checkout@v4
+          - name: Get Changed Files
+            id: changed-files
+            uses: tj-actions/changed-files@v44
+            with:
+              separator: ","
+              files: source/**
+          - name: Build Netlify Links for Changed Pages
+            id: build_page_links
+            run: |
+              new_links=""
+              base_link='https://deploy-preview-${{ github.event.number }}--docs-realm.netlify.app'
+              changed_files=${{ steps.changed-files.outputs.all_changed_files }}
+              files=$(echo $changed_files | tr "," "\n")
+              for file in $files; do
+                echo "processing ${file}"
+                if (! grep -s "includes/"  <<< $file) && 
+                    (! grep -s "images/"  <<< $file) && 
+                    (! grep -s "examples/"  <<< $file); then
+                  file="${file#source}"
+                  file="${file%.txt}"
+                  filenoslash="${file:1}"
+                  echo "${base_link}${file}"
+                  new_links+="<li><a href=${base_link}${file}>${filenoslash}</a></li>"
+                else
+                  echo "(file skipped)"
+                fi
+              done
+              if [ "$new_links" == "" ]; then
+                new_links="No pages to preview"
+              fi
+              echo "Final new_links string: "
+              echo "${new_links}"
+              echo "staging_links=${new_links}" >> "$GITHUB_OUTPUT"
+          - name: Update the PR Description
+            uses: MongoCaleb/pr-description-action@master
+            with:
+                regex: "<!-- start insert-links -->.*<!-- end insert-links -->"
+                appendContentOnMatchOnly: true
+                regexFlags: is
+                content: "<!-- start insert-links -->\n${{ steps.build_page_links.outputs.staging_links }}\n<!-- end insert-links -->"
+                token: ${{ secrets.GITHUB_TOKEN }}