Feature request: Serverless Rules support for sam validate linting

### Describe your idea/feature/enhancement

The team recently introduced the ability to use [cfn-lint](https://github.com/aws-cloudformation/cfn-lint) with `sam validate --lint`. This is great, but it does not support the ability to append rules like [**Serverless Rules**](https://github.com/awslabs/serverless-rules).

Serverless rules is a hugely beneficial[ rules set](https://awslabs.github.io/serverless-rules/rules/) that allows Serverless developers to run additional rules to validate infrastructure as code template against recommended Serverless best practices, across a numbers of AWS Services such as AWS Lambda, AWS Step Functions, Amazon API Gateway, Amazon SQS and SNS, Amazon EventBridge.

It would be great if we could provide a way to allow developers to append rules to sam validate linting capability.

### Proposal

In order to use Serverless Rules today developers need to installl the rules and append them directly to cfn-lint command

```
cfn-lint template.yaml -a cfn_lint_serverless.rules
```
it would be useful to do the same with sam validate

```
sam validate --lint --template myTemplate.yaml --append cfn_lint_serverless.rules
```

or include the Serverless Rules by default so no additional parameters need to be passed.

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

### Additional Details

https://awslabs.github.io/serverless-rules/