events: support SSM RunCommand

Hello,

It seems that we can't target an SSM Run Command with Events > **class Rule (construct)** :
https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.IRuleTarget.html

It's not obtainable from Ssm :
https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.RuleTargetConfig.html

### Use Case

I want to create scheduled Events Rule to Target an SSM RunCommand to call a Document, for example, to RunShellScript on my target(s) identified with Tags.

### Proposed Solution

Be able to configure SSM Run Command in Events.Rule, Yaml example :

```
TargetsProperties:
- Arn: "arn:aws:ssm:{{environment_config.region}}::document/AWS-RunShellScript"
Id: "1"
Input: "{
\"commands\":[ echo "Hello World" ]
}"
RoleArn: !stack_output ecs-host-cloudwatch-events-iam-role::RoleArn
RunCommandParametersProperties:
- Key: tag:UpdateECSAgent
Values:
- "true"

```

### Other

Done without pb & successfully with **events.CfnRule**.

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

---

This is a :rocket: Feature Request

Start with the events Rule target APIs, especially IRuleTarget and RuleTargetConfig, and compare their behavior with events.CfnRule. Trace how an SSM RunCommand target, document input, role, and tag-based parameters should be represented, then verify that a scheduled Rule can invoke the document with those settings.

Written by the indexing model from the issue text.