Support for third party tools (add datadog live tail link functionality to sam logs)

### Describe your idea/feature/enhancement

We want to add automatic Datadog live tail link generation to sam logs.

The user flow would look something like this:
```
sam logs --stack-name david-samcli-stack --datadog-livetail

This feature is currently in beta. Visit the docs page to learn more about the AWS Beta terms https://aws.amazon.com/service-terms/.
Enter Y to proceed with the command, or enter N to cancel:
[y/N]: y
Experimental features are enabled for this session.
Visit the docs page to learn more about the AWS Beta terms https://aws.amazon.com/service-terms/.

If your functions are instrumented with Datadog, use the following links to see datadog live tailed logs:
HelloWorldFunction: https://app.datadoghq.com/logs/link-to-your-livetail
HelloWorld1Function: https://app.datadoghq.com/logs/link-to-your-livetail
```

### Proposal

Currently ([existing PR](https://github.com/aws/aws-sam-cli/pull/3697)) I have integrated the new code directly into sam logs. A possible plugin based model was mentioned?

Things to consider:
1. Will this require any updates to the [SAM Spec](https://github.com/awslabs/serverless-application-model)

### Additional Details