feat(schedule-alpha): support customer managed KMS keys

[lpizzinidev]

Allows to specify a customer-managed KMS key for encryption.

Example:

declare const key: kms.Key;
declare const fn: lambda.Function;

const target = new targets.LambdaInvoke(fn, {
    input: ScheduleTargetInput.fromObject({
        "payload": "useful",
    }),
});

const schedule = new Schedule(this, 'Schedule', {
    schedule: ScheduleExpression.rate(Duration.minutes(10)),
    target,
    key,
});

Closes #27543.

---

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[kaizencc]

Thanks @lpizzinidev! Hopefully my minor nits don't break the build :)

[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]

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• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: b0ff6b6
• Result: SUCCEEDED
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[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).