chore(bedrock): add TwelveLabs Marengo 2.7 and Pegasus 1.2 (#35011)

### Issue # (if applicable)
None

### Reason for this change
https://aws.amazon.com/about-aws/whats-new/2025/07/twelvelabs-models-fully-managed-amazon-bedrock/

### Description of how you validated changes
```console
$ aws bedrock list-foundation-models --region us-east-1 --query 'modelSummaries[].modelId'   --output table
--------------------------------------------------
|              ListFoundationModels              |
+--------------------------------------------------+
...
|  twelvelabs.marengo-embed-2-7-v1:0             |
+--------------------------------------------------+
$ aws bedrock list-foundation-models --region us-west-2 --query 'modelSummaries[].modelId'   --output table
----------------------------------------------------
|               ListFoundationModels               |
+--------------------------------------------------+
...
|  twelvelabs.pegasus-1-2-v1:0                     |
+--------------------------------------------------+
```

### 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)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: phuhung273

packages/aws-cdk-lib/aws-bedrock/lib/foundation-model.ts

@@ -461,6 +461,12 @@ export class FoundationModelIdentifier {
   /** Base model "writer.palmyra-x5-v1:0". */
   public static readonly WRITER_PALMYRA_X5_V1_0 = new FoundationModelIdentifier('writer.palmyra-x5-v1:0');
 
+  /** Base model "twelvelabs.marengo-embed-2-7-v1:0". */
+  public static readonly TWELVELABS_MARENGO_EMBED_2_7_V1_0 = new FoundationModelIdentifier('twelvelabs.marengo-embed-2-7-v1:0');
+
+  /** Base model "twelvelabs.pegasus-1-2-v1:0". */
+  public static readonly TWELVELABS_PEGASUS_1_2_V1_0 = new FoundationModelIdentifier('twelvelabs.pegasus-1-2-v1:0');
+
   /**
    * Constructor for foundation model identifier
    * @param modelId the model identifier