Tags not applied to `AWS::Events::Rule`

Tag not applied to `AWS::Events::Rule` Ressource.

### Reproduction Steps

With following Stack:
```typescript
import cdk = require('@aws-cdk/core');
import events = require("@aws-cdk/aws-events");

export class CdkIssueEventsRuleTagsStack extends cdk.Stack {
constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);

const rule = new events.Rule(this, "ScheduleRule", {
schedule: events.Schedule.rate(cdk.Duration.hours(12)),
targets: []
});

cdk.Tag.add(rule, "MyTag", "ThatValue");
}
}
```

Synthesized template is:

```yaml
Resources:
ScheduleRuleDA5BD877:
Type: AWS::Events::Rule
Properties:
ScheduleExpression: rate(12 hours)
State: ENABLED
Metadata:
aws:cdk:path: CdkIssueEventsRuleTagsStack/ScheduleRule/Resource
CDKMetadata:
Type: AWS::CDK::Metadata
Properties:
Modules: aws-cdk=1.15.0,@aws-cdk/aws-events=1.15.0,@aws-cdk/core=1.15.0,@aws-cdk/cx-api=1.15.0,jsii-runtime=node.js/v12.12.0
Condition: CDKMetadataAvailable

[...]
```

In console, the Tags are available.

### Environment

Using CDK 1.15.0

---

This is :bug: Bug Report

Start with the TypeScript reproduction using events.Rule and synthesize the stack to compare the AWS::Events::Rule resource with the reported template. Trace how cdk.Tag.add is handled for that resource type; done means the synthesized resource includes the requested MyTag/ThatValue tags and the behavior is covered by an appropriate test.

Written by the indexing model from the issue text.