Draft: issue #162 - disable transit gateway attachment for ci

General MR

Summary

Add functionality in existing CI terraform to enable/disable AWS Transit Gateway attachments for RKE2 and EKS.

Relevant logs/screenshots

Successful pipeline runs:

RKE2 - https://repo1.dso.mil/big-bang/pipeline-templates/package-validation/-/pipelines/3274634 EKS - https://repo1.dso.mil/big-bang/pipeline-templates/package-validation/-/pipelines/3271450

Note: Unsuccessful BB down but appears unrelated.

Linked Issue

Issue #162