Use IAM role credential provider for lambda target

[zhiyanliu]

Fixes #56

Description

Fix the api create_mcp_gateway_target for lambda type.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Unit tests pass locally
• Integration tests pass (if applicable)
• Test coverage remains above 80%
• Manual testing completed

Checklist

• My code follows the project's style guidelines (ruff/pre-commit)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Security Checklist

• No hardcoded secrets or credentials
• No new security warnings from bandit
• Dependencies are from trusted sources
• No sensitive data logged

Breaking Changes

List any breaking changes and migration instructions:

N/A

Additional Notes

Add any additional notes or context about the PR here.

[icoxfog417]

This enhancement is crucial for implementing a starter toolkit for customized Lambda functions. Currently, the functionality is limited to default sample Lambda implementations only.

    def __handle_lambda_target_creation(self, role_arn: str) -> Dict[str, Any]:
        """Create a test lambda.

        :return: the targetConfiguration for the Lambda.
        """
        lambda_arn = create_test_lambda(self.session, logger=self.logger, gateway_role_arn=role_arn)

        return {
            "targetConfiguration": {"mcp": {"lambda": {"lambdaArn": lambda_arn, "toolSchema": LAMBDA_CONFIG}}},
            "credentialProviderConfigurations": [{"credentialProviderType": "GATEWAY_IAM_ROLE"}],
        }