utilizing the DOWNLOAD_TKRS environment variable in tanzu isolated-cluster download-bundle

[sukhotin]

Bug description

Unable to choose the desired TKR version(s) for downloading by tanzu isolated-cluster download-bundle command

Affected product area (please put an X in all that apply)

• ( ) APIs
• ( ) Addons
• ( ) CLI
• ( ) Docs
• ( ) IAM
• ( ) Installation
• ( X) Plugin
• ( ) Security
• ( ) Test and Release
• ( ) User Experience
• ( ) Developer Experience

Expected behavior
Option to choose the desired TKR version(s) for downloading by utilizing the DOWNLOAD_TKRS environment variable, similar to how it was done before the introduction of the tanzu isolated-cluster download-bundle command.
Steps to reproduce the bug

Version (include the SHA if the version is not obvious)

version: v0.29.0
buildDate: 2023-05-02
sha: b25b198-dirty

Environment where the bug was observed (cloud, OS, etc)
Ubuntu 22.04.2 LTS
Relevant Debug Output (Logs, manifests, etc)

[github-actions]

Hey @sukhotin! Thanks for opening your first issue. We appreciate your contribution and welcome you to our community! We are glad to have you here and to have your input on Tanzu Framework.