Allow cross tenant subscription rest api

**Related command**

`az rest --method post --uri "https://management.azure.com/subscriptions/customersubscription/resourceGroups/rg-managedapp/providers/Microsoft.Solutions/applications/mymanagedapp/listTokens?api-version=2018-09-01-preview"`

**Is your feature request related to a problem? Please describe.**

I have a managed app published, I want to retrieve the managed identity access token. This must be done with a publisher identity (or a managed identity in the managed resource group, but that is not the scenario I am playing). Unfortunately `az rest` first checks if the subscription is known before submitting the rest http call. The publisher identity does not see this subscription as it is connected with the consumer tenant.

**Describe the solution you'd like**

I would like to have a flag to skip the subscription check.

**Describe alternatives you've considered**

With `az account get-access-token` I can get a token, and then use regular `curl`.

**Additional context**

See https://learn.microsoft.com/en-us/azure/azure-resource-manager/managed-applications/publish-managed-identity#accessing-the-managed-identity-token where this is documented.