chore: Refactor context injection code by extracting two functions

[lym953]

What does this PR do?

Move the logic for Step Function context injection into

1. Lambda
2. nested Step Function

into two new functions.

Motivation

I will make the context injection logic more complicated and make the code longer, so let's split the function updateDefinitionString() for code readability.

Testing Guidelines

npm test

Additional Notes

Types of changes

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

Check all that apply

• [x] 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)
• [x] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog

[lym953]

/merge

[dd-devflow[bot]]

:steam_locomotive: MergeQueue: pull request added to the queue

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