Update URL to Upgrade Cautions in `puppet-enterprise-installer` output

The `puppet-enterprise-installer` links to https://puppet.com/docs/pe/2023.8/upgrading_pe.html#upgrade_cautions in its instructions:

```
Please read https://puppet.com/docs/pe/2023.8/upgrading_pe.html#upgrade_cautions before upgrading to PE 2023.8.0.
```

This URL has moved to https://www.puppet.com/docs/pe/2023.8/upgrade_cautions