docs: add PR to Projects using actions/add-to-project

See NordicSemiconductor/asset-tracker-cloud-docs#522

Author: coderbyheart

.github/workflows/add-to-project.yaml

@@ -1,18 +1,15 @@
-name: Add PRs to nRF Asset Tracker PR dashboard
+name: Add PRs to the nRF Asset Tracker Development project
 
 on:
   pull_request:
     types: opened
-env:
-  MY_GITHUB_TOKEN: ${{ secrets.AUTO_ASSIGN_ISSUE_TOKEN }}
 
 jobs:
   assign_to_project:
     runs-on: ubuntu-latest
     steps:
-      - name: Assign new pull requests to the Doing column of the project
-        uses: srggrs/[email protected]
-        if: github.event_name == 'pull_request'
+      - name: Add to project
+        uses: actions/add-to-project@main
         with:
-          project: "https://github.com/orgs/NordicSemiconductor/projects/2"
-          column_name: "Doing"
+          project-url: https://github.com/orgs/NordicSemiconductor/projects/3
+          github-token: ${{ secrets.AUTO_ASSIGN_ISSUE_TOKEN }}