Expose `GitRepository` attribute `is_disabled` to be able to disable the repo with the SDK and the Azure CLI

[camilo-s]

Currently this property is just carried along from the corresponding Repository property of the REST API (see e.g. https://learn.microsoft.com/en-us/rest/api/azure/devops/git/repositories/update?view=azure-devops-rest-7.2&tabs=HTTP#request-body)
This makes it impossible to leverage the Azure CLIs authentication flows to execute this operation. This feature would enable a number of downstream consumers, e.g. the Azure DevOps Terraform Provider: microsoft/terraform-provider-azuredevops#1138