docs(lambda-event-sources): add schema registry integration docs

[evzzk]

Issue # (if applicable)

Closes #34778.

Reason for this change

The AWS Lambda service recently added support for Schema Registry integration with Kafka event sources. This feature allows customers to use a schema registry (Confluent or Glue) to deserialize events from Kafka topics. While the CDK code support for this feature has been implemented, the documentation was incomplete, making it difficult for users to discover and properly configure this feature.

Description of changes

• Enhanced the Schema Registry documentation section in aws-lambda-event-sources README
• Added a comprehensive explanation of the feature and its requirements
• Added a note about IAM authentication requirements for MSK clusters
• Added detailed examples for both ManagedKafkaEventSource and SelfManagedKafkaEventSource
• Added information about required fields and automatic IAM permission generation
• Added a complete example that shows how to set up IAM permissions properly

Describe any new or updated permissions being added

No new permissions are being added in this PR. The documentation describes the existing permissions that are automatically generated when using Glue Schema Registry with Lambda.

Description of how you validated changes

• Verified that the documentation accurately reflects the current implementation
• Ensured the examples are consistent with the code implementation in schema-registry.ts
• Manually reviewed the updated documentation to ensure it matches the feature's behavior

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

[ozelalisen]

Build is failed due to JSII error, could you fix this:
@example must be code only, no code block fences allowed.

[ozelalisen]

Build is in failure mode

[mrgrain]

It is an usual pattern for readme examples. Consider if Stack and App are needed here and if they are adding anything to the examples. Typically that's only the case if you want to show interaction between multiple stacks.

Rosetta is failing because the example is inlined into this fixture: https://github.com/aws/aws-cdk/blob/c8d61c9929ef461ccafab2a6e90f11ce635c5750/packages/aws-cdk-lib/rosetta/aws_lambda_event_sources/default.ts-fixture

[mrgrain]

However, if you decide that a full example is the right way to go about this, you can add a new fixture into this directory that doesn't wrap the code inside a stack.

Then specify the fixture you want to use like this:

```ts fixture=some-fixture
new Stack();
```

See https://github.com/aws/jsii-rosetta?tab=readme-ov-file#fixtures

I'd still recommend that this new fixture contains as much of the setup as possible, e.g. like the imports of Stack and App.

[mrgrain]

Finally you may use nofixture, but that's really a last resort.

```ts nofixture
new Stack();
```

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 1bd28ad
• Result: FAILED
• Build Logs (available for 30 days)

Powered by github-codebuild-logs, available on the AWS Serverless Application Repository