How do you wait until a revision is ready before switching traffic to it?

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### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [ ] feature request
- [x] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

It seems once the github action kicks off to update the ARM resources, your container app will be offline/unresponsive until that new revision has fully started up. The previous revision's traffic will be revoked instantly even though the new revision is not ready