title: Firestore pre-deployment script
body: <p>I'm searching for a way to add pre-deployment scripts to my Firebase project.<br />
  I'm using Firestore and my security rules are set up in a way that only cloud functions can write to Firestore.</p>
  <p>I've added a user role field to my user table which automatically gets populated on userCreate. This works fine but my prod env still has users without this field.<br />
  A logical solution would be to run a pre-deploy command which add this field to all existing users but I have no clue how to do this.</p>
  <p>My current best solution is to create a cloud function specifically for this one-time use and trigger it.
  This doesn't feel like the right way to handle such things.<br />
  How do I run a one time update statement on Firestore?</p>