[Feature Request] az pipelines variable-group update should support batch variable updating

[jikuja]

Is your feature request related to a problem? Please describe. az pipelines variable-group update should support batch variable updating. Current process to do update requires deletions and/or multiple additions.

The current code-base seems does not accept variable setup as input for az pipelines variable-group update even underlying SDK and API supports that.

Describe the solution you'd like az pipelines variable-group update should get variables as optional input. Optionally passing data as JSON would be great.

Additional context

• https://learn.microsoft.com/en-us/rest/api/azure/devops/distributedtask/variablegroups/update?view=azure-devops-rest-6.0#request-body
• https://github.com/Azure/azure-devops-cli-extension/blob/master/azure-devops/azext_devops/devops_sdk/v6_0/task_agent/models.py#L3865-L3866