common job to choose m365 account (#3288)

<!-- PR description-->

Its a prerequisite for https://github.com/alcionai/corso/pull/3287
A common job which helps choosing m365 account using Round Robin.

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [x] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #<issue>

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

.github/workflows/accSelector.yaml

@@ -0,0 +1,46 @@
+name: SetM365AppAcc
+
+on:
+  workflow_call:
+    outputs:
+      client_app_slot:
+        value: ${{ jobs.GetM365App.outputs.client_app_slot }}
+      client_id_env:
+        value: ${{ jobs.GetM365App.outputs.client_id_env }}
+      client_secret_env:
+        value: ${{ jobs.GetM365App.outputs.client_secret_env }}
+
+jobs:
+  GetM365App:
+    environment: Testing
+    runs-on: ubuntu-latest
+    outputs:
+      client_app_slot: ${{ steps.roundrobin.outputs.CLIENT_APP_SLOT }}
+      client_id_env: ${{ steps.roundrobin.outputs.CLIENT_ID_ENV }}
+      client_secret_env: ${{ steps.roundrobin.outputs.CLIENT_SECRET_ENV }}
+    steps:
+      - name: Figure out which client id to use
+        id: roundrobin
+        run: |
+          slot=$((GITHUB_RUN_NUMBER % 4))
+          echo "CLIENT_APP_SLOT=$slot" >> $GITHUB_OUTPUT
+
+          case $slot in
+
+            0)
+              echo "CLIENT_ID_ENV=CLIENT_ID" >> $GITHUB_OUTPUT
+              echo "CLIENT_SECRET_ENV=CLIENT_SECRET" >> $GITHUB_OUTPUT
+              ;;
+            1)
+              echo "CLIENT_ID_ENV=CLIENT_ID_2" >> $GITHUB_OUTPUT
+              echo "CLIENT_SECRET_ENV=CLIENT_SECRET_2" >> $GITHUB_OUTPUT
+              ;;
+            2)
+              echo "CLIENT_ID_ENV=CLIENT_ID_3" >> $GITHUB_OUTPUT
+              echo "CLIENT_SECRET_ENV=CLIENT_SECRET_3" >> $GITHUB_OUTPUT
+              ;;
+            3)
+              echo "CLIENT_ID_ENV=CLIENT_ID_4" >> $GITHUB_OUTPUT
+              echo "CLIENT_SECRET_ENV=CLIENT_SECRET_4" >> $GITHUB_OUTPUT
+              ;;
+          esac