test: add condition to run RestApi's SecurityPolicy tests

[valerena]

This property is not available in all existing regions, so we need a dynamic condition to run these tests

Issue #, if available

• Tests added in feat: Support EndpointAccessMode property for AWS::Serverless::Api #3898 needed a condition so they run only where SecurityPolicy and EndpointAccessMode are correctly supported.

Description of changes

• Add new SECURITY_POLICY_REST_API "service", so we can check its availability before running related tests.

Description of how you validated changes

• make pr only for now.

Checklist

• Review the generative AI contribution guidelines
• Adheres to the development guidelines
• Add/update transform tests
  • Using correct values
  • Using wrong values
• Add/update integration tests

Examples?

Please reach out in the comments if you want to add an example. Examples will be
added to sam init through aws/aws-sam-cli-app-templates.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.