fix: Move Go module to another repo

[lym953]

What does this PR do?

The existing plan is to keep the generated Go module in this repo. This PR makes it untracked from git in this repo, and updates the module path to a separate repo datadog-cdk-constructs-go.

Motivation

1. The build command for Go package generates a file like datadog-cdk-constructs-v2-1.13.0.tgz (among others), which is 1.40MB and is part of the package. As a result, whenever we make a small change, a new tgz file will be generated and tracket by git. This is unnecessary, as we only need to upload the tgz file for tagged versions (releases). We want to change it so that a tgz file is only generated when we actually want to release a new version.
2. By searching in GitHub, we see that it's a common practice to put the generated Go module in a separate repo.

Testing Guidelines

Tested by using this Go module in an example CDK stack in #273.

Additional Notes

Next steps:

1. Update README.md by adding instructions for Go
2. Clean up unused files on the root level of datadog-cdk-constructs-go repo
3. Add the Go release script to publish_prod.sh to make release more automated
4. Maybe release a new version

Feature Request: Datadog CDK Construct for Go

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

[buraizu]

Approving, README.md still renders as expected in local build

[lym953]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in main is 4m.

Use /merge -c to cancel this operation!