feat(aws-servicecatalogappregistry-alpha): add attributes property to AttributeGroup import

[naaa760]

Closes #35524.

Reason for this change

• The current fromAttributeGroupArn method only creates a reference to an existing AttributeGroup but doesn't provide access to the stored attributes. This limits the usefulness of AttributeGroups as a centralized configuration store, forcing users to use SSM parameters for sharing configuration objects across multiple accounts.

Description of changes

• Added an optional attributes parameter to the fromAttributeGroupArn method and added an attributes property to the IAttributeGroup interface. This allows users to provide attributes when importing an AttributeGroup, enabling access to stored configuration data.

Changes made:

• Added attributes?: { [key: string]: any } property to IAttributeGroup interface
• Added attributes property to AttributeGroupBase abstract class
• Updated fromAttributeGroupArn method signature to accept optional attributes parameter
• Added attributes property to concrete AttributeGroup class
• Updated constructor to set the attributes property from props

Design decisions:

• Made attributes optional to maintain backward compatibility
• Used the same type { [key: string]: any } as the existing AttributeGroupProps.attributes
• No breaking changes to existing API

Describe any new or updated permissions being added

• No new IAM permissions are required. This change only affects the CDK construct interface and doesn't modify AWS resource permissions.

Description of how you validated changes

• Added unit tests to verify importing AttributeGroup with and without attributes
• Added test to verify accessing attributes from newly created AttributeGroup
• All existing tests continue to pass, ensuring backward compatibility

[aws-cdk-automation]

The pull request linter fails with the following errors:

❌ Features must contain a change to an integration test file and the resulting snapshot.
❌ The title scope of the pull request should omit 'aws-' from the name of modified packages. Use 'servicecatalogappregistry-alpha' instead of 'aws-servicecatalogappregistry-alpha'.

If you believe this pull request should receive an exemption, please comment and provide a justification. A comment requesting an exemption should contain the text Exemption Request. Additionally, if clarification is needed, add Clarification Request to a comment.

[naaa760]

Hello @pahud
would you please review this PR?