[aws-events-targets][aws-inspector] Ability to schedule runs for assessment template

Currently, there is no way to schedule assessment run Inspector's template, neither via `@aws-cdk/aws-inspector` nor via @aws-cdk/aws-events-targets.

### Use Case
We are setting up Inspector (Assessment Template and Assessment Target) via CDK and we would like to schedule assessment runs for the template.

### Proposed Solution
Option 1: Add new property(e.g., `schedule`) for `CfnAssessmentTemplate` in `@aws-cdk/aws-inspector`
Option 2: New events target (InspectorAssesmentTemplate) in `@aws-cdk/aws-events-targets`

* [ ] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

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This is a :rocket: Feature Request

Start by examining the AWS Inspector support in @aws-cdk/aws-inspector and the target integrations in @aws-cdk/aws-events-targets. Verify which proposed approach matches Inspector's scheduling capabilities and define the public API needed so users can schedule assessment template runs through CDK.

Written by the indexing model from the issue text.