fix(elasticache): the default engine for NoPasswordUser contradict in the docs

[mazyu36]

Issue # (if applicable)

Closes #35847

Reason for this change

NoPasswordUser only supports the Redis engine, but the documentation incorrectly states that the default engine is VALKEY, creating a contradiction between the implementation and documentation. Since NoPasswordUser only works with Redis, the engine property should not be configurable for this user type.

Description of changes

• Fixed the contradiction by removing the engine configuration option from NoPasswordUser.
• The engine property was moved from the base user class to only the user types that actually support multiple engines (IamUserProps and PasswordUserProps).

Describe any new or updated permissions being added

No new or updated IAM permissions are being added with these changes.

Description of how you validated changes

• Verified that all existing unit tests pass after the changes
• Updated test cases to remove references to the now-removed engine property in NoPasswordUser tests

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

BREAKING CHANGE: The engine property in NoPasswordUserProps has been removed.

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

[aws-cdk-automation]

The pull request linter fails with the following errors:

❌ Fixes must contain a change to an integration test file and the resulting snapshot.

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.

✅ A exemption request has been requested. Please wait for a maintainer's review.

[mazyu36]

Exemption request: Only changes to the setting method of the property, sufficient with unit tests.