(synthetics): add tracing

Enable active tracing (https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-synthetics-canary-runconfig.html#cfn-synthetics-canary-runconfig-activetracing) for a canary.

### Use Case

End-to-end tracing from Canary to API Gateway to Lambda.

### Proposed Solution

Add a new property to `synthetics.CanaryProps`:

```
new synthetics.Canary(this, 'MyCanary', {
...,
activeTracing: true,
})
```

By default, it will be `false`. When set to true, it will also append XRay permissions to the IAM role (e.g. the managed policy `arn:aws:iam::aws:policy/AWSXrayWriteOnlyAccess`).

### Other

Similar PR: https://github.com/aws/aws-cdk/pull/11865.

* [X] :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 at the TypeScript implementation of the synthetics.Canary construct and its CanaryProps, then inspect how the canary run configuration and IAM role are defined. Compare the activeTracing CloudFormation setting with the linked AWS documentation and ensure the X-Ray write permission is added only when enabled; done means the property defaults to false and supports end-to-end tracing.

Written by the indexing model from the issue text.