New Pattern: aws-codepipeline-step-functions

Build a new pattern to use AWS Step Functions as an action for AWS CodePipeline stage.

### Use Case

Need this feature to invoke AWS Step Functions for AWS Codepipeline stage.

### Proposed Solution

Create a CodePipeline, CodePipeline stage, codepipeline action to invoke the step function.

* [X] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

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This is a :rocket: Feature Request

No files or tests are named. Start by reviewing existing AWS Solutions Constructs patterns for CodePipeline stages and Step Functions, then identify the pattern entry points and test conventions. Done means a new pattern can create a CodePipeline action that invokes a Step Function and is covered by the repository's established validation.

Written by the indexing model from the issue text.