feat(appsync): support DEBUG and INFO logging levels for AppSync GraphQL APIs (#31326)

### Issue # (if applicable)

N/A

### Reason for this change
AppSync now support `DEBUG` and `INFO` logging levels.

Announcement: [AWS AppSync enhances API monitoring with new DEBUG and INFO logging levels](https://aws.amazon.com/about-aws/whats-new/2024/09/aws-appsync-api-monitoring-debug-info-logging-levels/)



### Description of changes
* Added `INFO` and `DEBUG` to the FieldLogLevel enum.
* Added README, unit tests, and integration tests for FieldLogLevel as they were missing.



### Description of how you validated changes
Add unit tests and integ test.


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: mazyu36