[Bug]: Config file does not throw error at multiple entities with same definition name

### What happened?

Currently we can add multiple entities that have the same definition name under the `entities` property. Only one of these entities will be used, the others are discarded while the deserialization takes place. This means that DAB never throws an error or a warning regarding these repeated entities, and when we use the `dab validate` command the validation succeeds.

### Version

2.0.0-rc

### What database are you using?

Azure SQL

### What hosting model are you using?

Local (including CLI)

### Which API approach are you accessing DAB through?

_No response_

### Relevant log output

```Text

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### Code of Conduct

- [x] I agree to follow this project's Code of Conduct