[Feature Request] AWS Managed Knowledgebases

## Describe the solution you'd like

It would be great, if the app would also support the API of AWS managed knowledge bases.

## Why the solution needed

AWS managed knowledge bases have more options for connecting third-party data sources and the Preview connectors in the self-managed KBs will be sunsetted.

## Additional context

n/a.

## Implementation feasibility

Are you willing to collaborate with us to discuss the solution, decide on the approach, and assist with the implementation?

- [ ] Yes, I am able to implement the feature and create a pull request.
- [x] No, I am unable to implement the feature, but I am open to discussing the solution.

No files, tests, or entry points are named. Start by reviewing the existing self-managed knowledge-base integration and the AWS managed knowledge bases API, then define the supported workflows and acceptance criteria before implementation; done means the app supports the agreed managed-knowledge-base operations.

Written by the indexing model from the issue text.