fix(events): cannot specify a custom id on rule targets

[tskawada]

Issue # (if applicable)

Closes #37025.

Reason for this change

The Id of an EventBridge Rule target is always auto-generated as Target0, Target1, ...
There is no way for users to specify a custom target id through the L2 Rule.addTarget API, even though the underlying PutTargets API allows it.
As a result, infrastructure imported into CDK that was originally created with a custom target id is reported as drifted by CloudFormation, since CDK overwrites the id at synth time.

Description of changes

Added an optional second argument AddTargetOptions to Rule.addTarget(target, options?) with an optional id field.
When provided, it is used as the CloudFormation target Id and takes precedence over both the auto-generated id and the deprecated RuleTargetConfig.id returned from IRuleTarget.bind(). The id is validated against the EventBridge constraints (1–64 chars, [A-Za-z0-9._-]); tokens are passed through.

The id passed to IRuleTarget.bind(rule, id) is intentionally left as the auto-generated id so derived resources (IAM roles, log groups, etc.) keep their existing logical ids. This keeps the change strictly opt-in.

The @deprecated note on RuleTargetConfig.id was updated to point to the new option, and a short Custom Target Id section was added to the aws-events README.

Alternatives considered: enriching RuleProps.targets with a { target, id } shape (rejected: public type change), and passing
the user id to bind() (rejected: would change derived resource logical ids for existing stacks).

Describe any new or updated permissions being added

N/A. Synth-time only; no runtime IAM permissions are added.

Description of how you validated changes

Added unit tests in aws-events/test/rule.test.ts covering: custom id is rendered, mixed custom and auto-generated ids, user id beats RuleTargetConfig.id, all allowed characters, validation failures (empty / too long / invalid chars), and Token ids deferred to synth.
All 345 existing aws-events tests continue to pass. Full aws-cdk-lib build (eslint, pkglint, awslint) passes.

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

[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.

[tskawada]

Exemption Request

This change adds an optional opt-in property whose effect is limited to a single string field of the synthesized loudFormation template (AWS::Events::Rule.Targets[].Id). The output is fully verified by unit tests using Template.fromStack().hasResourceProperties(). No runtime behavior, IAM permissions, or new dependencies are introduced, so an integration test would only re-verify what CloudFormation already guarantees for the field's character set. Requesting an exemption from the integration test requirement.