Added `getMessage` function under ai subpath

[yuhengshs]

Problem

Issue number, if available:

Changes

• Added getMessage function to leverage ConverseCommand from Bedrock API
• Added types to align with ConverseCommand use case.
• Added unit tests for Valid input handling, Different content types processing, Multiple message conversation handling and Invalid input error throwing

Corresponding docs PR, if applicable:

Validation

Checklist

• [ ] If this PR includes a functional change to the runtime behavior of the code, I have added or updated automated test coverage for this change.
• [ ] If this PR requires a change to the Project Architecture README, I have included that update in this PR.
• [ ] If this PR requires a docs update, I have linked to that docs PR above.
• [ ] If this PR modifies E2E tests, makes changes to resource provisioning, or makes SDK calls, I have run the PR checks with the run-e2e label set.

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

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 5f7472cf6a36d9b3867e7475c2815d12051a0522

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@aws-amplify/backend-ai	Minor
@aws-amplify/backend	Minor

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