Fix Cosmos GSI live test secret plumbing

[tvaron3]

Description

Adds explicit variable-group support to the Python live-test archetype and imports Test Secrets for Cosmos Live Tests - user administered for Cosmos live tests.

This allows gsi-pipeline-uri and gsi-pipeline-key to resolve before they are mapped to GSI_ACCOUNT_HOST and GSI_ACCOUNT_KEY. Previously, build 6548102 passed the literal $(gsi-pipeline-key) to the SDK, causing binascii.Error: Incorrect padding during GSI test setup.

The plumbing follows the existing Azure SDK for Rust pattern.

Testing

• Parsed both modified YAML files successfully.
• Verified the diff with git diff --check.

[github-actions]

Hi @tvaron3. Thank you for your interest in helping to improve the Azure SDK experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment. Otherwise, we'll close this out in 7 days.

[github-actions]

Hi @tvaron3. Thank you for your contribution. Since there hasn't been recent engagement, we're going to close this out. Feel free to respond with a comment containing /reopen if you'd like to continue working on these changes. Please be sure to use the command to reopen or remove the no-recent-activity label; otherwise, this is likely to be closed again with the next cleanup pass.