Broken link in documentation in content/reference/validator/rules/unique.md

### Package version

latest

### Describe the bug

The text 
```
The validation rule is added by @adonisjs/lucid package. So make sure it is [installed and configured](https://github.com/adonisjs/v5-docs/blob/develop/content/guides/database/setup.md), before using this rule.
```

is linking to a file/page that no longer exists

### Reproduction repo

_No response_