k8s tutorial: example charm sets status to active too optimistically

Our official solution correctly goes into the blocked state when not integrated with PostgresSQL.

When it is integrated, it's all too eager to get to work... even when Postgres is clearly not ready:

```
App Version Status Scale Charm Channel Rev Address Exposed Message
demo-api-charm active 1 demo-api-charm 0 10.152.183.177 no
postgresql-k8s waiting 0/1 postgresql-k8s 14/stable 495 no installing agent

Unit Workload Agent Address Ports Message
demo-api-charm/0* active idle 10.1.0.72
postgresql-k8s/0 waiting allocating installing agent
```

The integration test is generally OK, because we wait for all apps to become active and thus for Postgres too.