Support specifying custom tenant ID/domain for authentication

Yes. When using the VSCode AKS Tools extension, I’m always redirected to the default Azure login page for authentication. However, in my organization, we use a custom Azure Active Directory tenant/domain. Currently, there is no way to specify a custom tenant ID or domain.

Platform: `vscode`

**Describe the solution you'd like**
I'd like to have an option to configure a **custom tenant ID** or **login domain** before triggering the Azure authentication flow. This could be done via:

* VSCode settings (e.g., `aks-tools.tenantId`)
* Environment variable
* UI prompt when initiating login

Start by tracing the VSCode AKS Tools extension's Azure authentication flow. Compare how VSCode settings, environment variables, and the login prompt could provide a custom tenant ID or login domain, then verify that the selected value is used when authentication starts. Done means users can authenticate against a non-default Azure tenant or domain.

Written by the indexing model from the issue text.