fix(amazonq): Q chat stopped using IAM creds in the Amazon Q v1.63.0 release

[floralph]

Problem

Amazon Q for VSCode fails to authenticate in SageMaker environments after v1.62.0. The extension moved from directly calling the Q service using AWS SDK clients to using the aws-lsp-codewhisperer service (LSP). While the legacy
implementation had specific handling for SageMaker IAM credentials, the new LSP-based implementation only supports SSO token authentication.

The breaking change occurred in commit 938bb37 which enabled three experiment flags by default, moving the extension from the core implementation to the LSP implementation that lacks IAM credential
support.

Solution

This PR adds IAM authentication support to the Amazon Q LSP client for SageMaker environments by:

1. Setting the USE_IAM_AUTH environment variable when running in SageMaker to signal the language server to use IAM authentication mode
2. Enhancing the AmazonQLspAuth class to handle both SSO and IAM authentication flows, with proper credential retrieval and encryption
3. Updating client initialization to indicate IAM credential support when running in SageMaker environments
4. Adding connection metadata handling for IAM authentication with appropriate fallback values
5. Implementing early auto-login for SageMaker IAM credentials during LSP activation

The solution maintains backward compatibility with existing SSO authentication while enabling IAM credential support specifically for SageMaker environments, restoring the functionality that was available in the legacy core
implementation.

[github-actions]

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