Document step function support

[YuviGold]

What does this PR do?

Add to the documentation that Step Functions forwarding to Datadog is supported since version 3.46.0 by #546

Motivation

Recently tried to subscribe my Step Function's Cloudwatch log group to the Datadog Forwarder lambda.
Logs looked great but the logs weren't received by the DataDog server.
Eventually, I figured my DataDog Forwarder version was old (3.44.0).

In general, it wasn't mentioned that a step function is supported though I was able to saw it can be used on some articles on the web.
It would have been really helpful to know from the official docs that:

1. Step Functions are supported by the DataDog Forwarder
2. A minimum version is required.

Testing Guidelines

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)
• This PR passes the unit tests
• This PR passes the installation tests (ask a Datadog member to run the tests)