enable manual Template Schema upgrades (#163)

Author: PatMyron

.github/workflows/template-schema-updater.yaml

@@ -1,6 +1,7 @@
 on:
   schedule:
     - cron: '*/5 * * * *'
+  workflow_dispatch: # Enables on-demand/manual triggering: https://docs.github.com/en/free-pro-team@latest/actions/managing-workflow-runs/manually-running-a-workflow
 jobs:
   job:
     runs-on: ubuntu-latest