🥕[Bug]: Update `validate` to catch 2 roles with the same name.

### What happened?

This should be illegal.

```json
{
"$schema": "https://github.com/Azure/data-api-builder/releases/download/v1.3.19/dab.draft.schema.json",
"data-source": {
"database-type": "mssql"
"options": {
"set-session-context": false
}
},
"runtime": {
"rest": {
"enabled": true,
"path": "/api",
"request-body-strict": true
},
"graphql": {
"enabled": true,
"path": "/graphql",
"allow-introspection": true
},
"host": {
"cors": {
"origins": [],
"allow-credentials": false
},
"authentication": {
"provider": "StaticWebApps"
},
"mode": "development"
}
},
"entities": {
"User": {
"source": {
"object": "dbo.User",
"type": "table"
},
"permissions": [
{
"role": "anonymous",
"actions": [
{
"action": "*"
}
]
},
{
"role": "jerry",
"actions": [
{
"action": "*"
}
]
},
{
"role": "jerry",
"actions": [
{
"action": "*"
}
]
}
]
}
}
}
```

### Version

1.4

### What database are you using?

Azure SQL

### What hosting model are you using?

_No response_

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

_No response_

### Relevant log output

```Text

```

### Code of Conduct

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