docs(appsync): add placeholder Query type for improved schema compatibility

[azarboon]

Issue # (if applicable)

Closes #.

Reason for this change

My earlier PR (#32633) addressing the same issue was approved but encountered sync problems, leading me to close it and open this fresh PR. I’ve ensured this branch is properly synced, and I hope the issue is resolved.

For clarity, the rationale behind this change is as follows:

While the current schema is technically valid with a single root Mutation type, most GraphQL clients and tools expect a default Query operation for introspection and standard queries. This PR introduces a minimal placeholder Query type to enhance compatibility and align with widely accepted GraphQL conventions.

Description of changes

Describe any new or updated permissions being added

<!— What new or updated IAM permissions are needed to support the changes being introduced ? -->

Description of how you validated changes

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

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

[azarboon]

@kaizencc, since you've already reviewed the content in the previous PR, could you please approve this one as well?

[kaizencc]

Thanks @azarboon! I'll keep an eye on it and make sure this gets merged :)

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.64%. Comparing base (d48d77a) to head (755771b).
Report is 1 commits behind head on main.

Additional details and impacted files

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##             main   #32652   +/-   ##
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  Coverage   80.64%   80.64%           
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  Files         107      107           
  Lines        6996     6996           
  Branches     1290     1290           
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  Hits         5642     5642           
  Misses       1175     1175           
  Partials      179      179           

Flag	Coverage Δ
suite.unit	80.64% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	80.64% <ø> (ø)

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 755771b
• Result: SUCCEEDED
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[mergify]

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