[BUG] OpenSearch dashboards is not accesible for console user

## 🚨 **Please Note** 🚨

To ensure efficient investigation of the issue, please fill out the fields below with as much detail as possible. **Reports that do not follow this template may be closed without notification.** We appreciate your cooperation.

## Describe the bug

With Bedrock Knowledge Bases on custom bot, users can't access OpenSearch dashboard although user has AdministratorAccess.

There are no data access control granted to IAM Roles or Users used by human. It might be a good idea to be able to configurable the OpenSearch dashboard administrator role or user in cdk.json.

## To Reproduce

Steps to reproduce the behavior:

1. Create custom bot with knowledges
2. Go to OpneSearch Serverless collection page on AWS Management Console
3. Click on 'dashboard' link
5. See error

## Screenshots


## Additional context

Add any other context about the problem here.

Review the Bedrock Knowledge Bases and OpenSearch Serverless setup, starting with the cdk.json configuration mentioned in the report. Reproduce the dashboard access failure after creating a custom bot with knowledge, then trace the IAM roles or users used by human operators. Done means console users can access the OpenSearch dashboard with the intended administrator configuration.

Written by the indexing model from the issue text.