feat(rds): enable grantDataApiAccess method for imported database cluster (#31280)

### Issue # (if applicable)

Closes #31116 .

### Reason for this change



It was not possible to call the `grantDataApiAccess` method for an imported database cluster.

Because the imported database cluster always has the `enableDataApi` with false.

https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-rds/lib/cluster.ts#L983

```ts
class ImportedDatabaseCluster extends DatabaseClusterBase implements IDatabaseCluster {
  // ...
  protected readonly enableDataApi = false;
```

But the `grantDataApiAccess` throws an error when the `enableDataApi` is set to false.

https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-rds/lib/cluster.ts#L523-L526

```ts
  public grantDataApiAccess(grantee: iam.IGrantable): iam.Grant {
    if (this.enableDataApi === false) {
      throw new Error('Cannot grant Data API access when the Data API is disabled');
    }
    // ...
}
```

### Description of changes



Added the property `dataApiEnabled` to attributes for the imported database cluster.

If the `dataApiEnabled` to the attributes is set to true, the `enableDataApi` in the imported cluster will be set to true and the `grantDataApiAccess` can be called.

### Description of how you validated changes



Unit and integ tests.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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Author: go-to-k