chore: Refactor example Go stack by splitting a function

[lym953]

What does this PR do?

Right now NewAppStack() creates a stack and integrates it with Datadog. This PR splits into two functions:

1. NewAppStackWithoutDatadog(): creates a stack, without Datadog integration
2. NewAppStackWithDatadog(), which calls NewAppStackWithoutDatadog() and adds Datadog integration

Motivation

I'm going to rename the interfaces like I did in https://github.com/DataDog/datadog-cdk-constructs/pull/288. To make sure both the new API and old API work, I will need to to write two stacks for testing the two APIs. The two stacks will share the non-Datadog setup code, so I'm putting this part in the NewAppStackWithoutDatadog() function.

Testing Guidelines

cdk deploy successfully deploys the Go stack.

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)
• [ ] 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

The median merge time in main is 4m.

Use /merge -c to cancel this operation!